Cristiano Ronaldo is back at Manchester United and ready to wear the club's No. 7 shirt for the first time since 2009 in Saturday's Premier League clash against Newcastle United at Old Trafford. But giving the Portugal forward his old number is the easy part for United; the big challenge now is where to play him.

United manager Ole Gunnar Solskjaer is the man who must solve the Ronaldo dilemma, and it's not an easy one to fix. If he gets it right, Solskjaer will give a huge boost to his prospects of guiding United to their first major trophy since 2017 and, at the same time, turbo-charge his team's goal-scoring output. But if Solskjaer gets it wrong, he risks a domino effect of disenchantment and loss of form among his other attacking players.

With Ronaldo becoming one of six international forwards in the United squad, alongside Marcus Rashford, Edinson Cavani, Mason Greenwood, Jadon Sancho and Anthony Martial, Solskjaer must not only ensure he keeps them all happy, but also get the right formula with his attacking game plan. He must also find a way to make sure that Ronaldo's presence in the team does not have a negative impact on the performances of midfielders Bruno Fernandes and Paul Pogba.

But while signing one of the world's most reliable goal scorers brings so many positives to United, Solskjaer needs to make it work and deploy the former Real Madrid and Juventus forward in the position that gets the best out of him and his teammates.

So where will Ronaldo play, and what are the positives and negatives of each possible position?

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Centre-forward

During his final season at Juventus, Ronaldo spent 92% of his time on the pitch in a centre-forward role, with the majority of those on the left side of a front two alongside either Paulo Dybala or Alvaro Morata. He ended up with 36 goals in 44 appearances in all competitions for Juve, so his ability to convert chances remained hugely impressive.

During his record-breaking display for Portugal against Republic of Ireland last week, when he scored two late headers to win the game and move clear of Iran's Ali Daei as the all-time leading scorer in men's international football, Ronaldo started in a central role. After a half-time tactical switch, Ronaldo moved to the left once Andre Silva introduced as centre-forward.

From that brief snapshot against the Irish, when Brighton & Hove Albion's Shane Duffy and Sheffield United's John Egan shared duties marking Ronaldo in a back three, the 36-year-old struggled to make an impact against the defenders as a lone striker. It was only the arrival of Silva in the second half that allowed Ronaldo more freedom to roam across the forward line.

If Solskjaer chooses to use Ronaldo centrally for United, he will have to play him alongside a centre-forward as Juventus did, and as Portugal eventually did against Ireland. Cavani is the most accomplished centre-forward on United's books, but at 34, he is neither a long-term solution nor one who could be expected to form a 40-50 game partnership with the Portugal star. Cavani would undoubtedly offer excellent qualities as an unselfish strike partner, but how often could he play?

Beyond Cavani, Martial's work rate and ability to provide a physical foil for Ronaldo are questionable, while neither Rashford nor Greenwood enjoy the central role or the stress of playing with their back to goal. So while a central role is the best option, Solskjaer's potential solutions aren't ideal.

Wide left

According to Transfermarkt.com, Ronaldo has played the majority of his club career on the wide left of a front three -- 394 of his games have been in this position, and he's scored 365 goals in that role. But just 7% of Juventus appearances were from wide on the left last season. During the 2019-20 season, 51.3% of Ronaldo's Juve outings came on the left.

At 36, Ronaldo remains an incredible athlete, but he's no longer a player who will sprint down the wing and look to beat his marker by taking him on, and that is perhaps why he has now moved away from his traditional position. Yet at United, with Luke Shaw taking care of defensive duties behind him and the pace of Rashford, Sancho and Greenwood alongside him in the forward line, Ronaldo could switch back to his old position at Old Trafford. His ability to cut inside and shoot with his right foot remains undimmed, but opponents would quickly learn that Ronaldo will only go one way: inside. Still, that's been no secret for many years and few teams have discovered a way to stop him being a threat.

However, playing Ronaldo out left would have an impact on Rashford's place in the team. The England forward is still recovering from preseason shoulder surgery and will be unavailable for at least another month, but once he is fit, he will expect to play and wide left is where he is most effective. Using Ronaldo out wide and deploying Rashford through the middle is an alternative option, but Rashford has struggled to make a consistent impact as a central striker and his natural instinct is to drift wide and cut inside.

Playing Ronaldo on the left would be a problem because he has moved away from that role over the past 12 months, and it would also have a negative impact on Rashford.

Wide right

Ronaldo has played 135 of his club games as a right winger, but the majority of those were during his younger days at United when he shared attacking duties with Wayne Rooney, Ruud van Nistelrooy and Louis Saha. Back then, he had the electric pace and trickery to beat a defender and cross into the penalty area, but his game has developed since those formative days.

Having spent £73 million to sign Sancho from Borussia Dortmund this summer and end their search for a top-quality right winger, it would make little sense for Solskjaer to tell Ronaldo to play in that position. He rarely played in that role for Juventus and it's a position he's unlikely to take for United, but that is not to say that Ronaldo can't still perform down the right.

He could still cut inside and shoot with his left foot, which has become almost as reliable as his right, and his delivery would enable him to whip in crosses for the likes of Cavani, Martial and Rashford. But it would be a waste of Ronaldo's best qualities if Solskjaer chose to use him wide right for anything more than a brief spell during a game.

No. 10 role

Let's be clear: Solskjaer is not going to select a team that has Cristiano Ronaldo playing as a No. 10. With Bruno Fernandes, Paul Pogba and Juan Mata all highly capable and effective in that creative role behind the forwards, it would require a major injury crisis or a pile-up of suspensions for Solskjaer to even consider it. But while Ronaldo won't start as a No. 10, the danger to United comes with his tendency to drop deep and go in search of the ball if the game is going against his team or his goal-scoring chances have dried up.

While playing for Portugal against Ireland in Faro, when he did not score his first goal until the 89th minute, Ronaldo became increasingly frustrated with the course of the game and began to drop into the No. 10 position early in the second half. In doing so, he encroached upon the space occupied by Fernandes and nullified his new club teammate to such an extent that Portugal coach Fernando Santos substituted the United midfielder after just 62 minutes.

It is no secret that Fernandes often struggles to shine for Portugal as he has done for Sporting Lisbon and United and this could be, to some extent, a direct consequence of Ronaldo's presence in the final third. Coach Santos consistently prefers Manchester City's Bernardo Silva to Fernandes, but with Bernardo operating on the wide right, he is able to perform without Ronaldo suffocating his space. If Ronaldo chooses to roam free at United and drop into Fernandes' role, there is a risk of United's most consistent player being impacted negatively. The same could happen to Pogba if the France midfielder is played as a No. 10.

So while it's not a position in which he will start, Ronaldo could certainly hurt United's creativity in attacking midfield if Solskjaer fails to keep him disciplined in a positional sense.

Impact substitute

Ronaldo made 292 appearances for United during his first spell at the club and 48 of those came as a substitute, including his debut against Bolton Wanderers in August 2003. But once he became a first-team regular, he started whenever he was fit and the eight substitute appearances he made during his final two seasons under Sir Alex Ferguson were following injury or as a result of being rested ahead of more significant games in the Champions League or Premier League.

For the past 10 years, Ronaldo has been a starter wherever he has played, and it was his relegation to the substitutes' bench for Juventus' Serie A game against Udinese last month that signalled his time in Turin was over. So it's highly unlikely that Solskjaer will assess his attacking options and decide that Ronaldo is only good enough to start on the bench, though such a move could have its merits.

There are few better players in the game when it comes to taking advantage of tiring defences to score late goals; a fresh Ronaldo over the final 20-30 minutes of games could make him a lethal impact substitute for United. And Solskjaer has plenty of alternative options to use up front, so there could be times when it makes sense to start with Ronaldo on the bench.

Ferguson would have the strength of character and respect of the squad (and Ronaldo) to name him on the bench, but does Solskjaer possess the same ability to make such a big call? Unlikely.

Conclusion

Everything points to Ronaldo's best position now being that of a central striker who plays slightly to the left of a front two. That is where he has played most in recent months and where his goals have come from, but the problem for United is that they rarely -- if ever -- play with two up top.

To get the best out of Ronaldo, Solskjaer needs to use a striker who will occupy the central defenders so Ronaldo is able to move around the attacking third and score goals. He has that man in Cavani, but as mentioned earlier, it is a Cavani in his mid-30s rather than the Uruguay international in his peak years at Napoli and Paris Saint-Germain.

Initially, it is likely that Ronaldo will play on the left and drift inside, operating largely within the central channel of the pitch. But once Rashford is fit, he may move inside and that will only work if he has a Cavani alongside him. So there is no perfect solution or flawless plan, unless Solskjaer has a tactical solution that will surprise us all.