MANCHESTER, England -- There is no hiding place in the Champions League. If you are not ruthless and decisive in key moments, the only guarantee is that you will pay a heavy price. It gets even worse when you throw naivety into the mix, as Ole Gunnar Solskjaer and Manchester United discovered to their cost with a 3-1 home defeat against Paris Saint-Germain on Wednesday.

United have shown great promise at times in the Champions League this season by winning in Paris and beating RB Leipzig 5-0, but they have also displayed inexperience and ineptitude -- the shambolic defending while losing to Istanbul Basaksehir was a particular low point -- and the shortcomings of their players and manager came to the fore once again against PSG.

Solskjaer's side went into this Group H clash knowing that a draw would secure qualification for the round of 16 ahead of next week's trip to Leipzig. But missed chances by United's forwards and an inexplicable decision by Solskjaer not to substitute midfielder Fred when he was walking headlong into an inevitable red card enabled PSG to claim the victory that revives their own qualification hopes and leaves United needing to avoid defeat in Germany on Tuesday in order to make it through to the knockout stages.

They may have to do it without Marcus Rashford too, with the forward being forced off with a shoulder injury late in the second half.

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"We go into a game wanting to win," Solskjaer said after the match. "The games against PSG and Leipzig show how much we've developed in these types of games. It was just about finishing today."

Solskjaer's United team has proven to be so spectacularly unpredictable that it would be foolish to bet against any result when they face Julian Nagelsmann's side in six days' time, but they really shouldn't be travelling to that game in need of a point to qualify.

Last month's defeat in Istanbul now looks hugely damaging to United's hopes, with the Turkish outfit losing every other game in the group. That loss left United vulnerable to another setback and PSG ensured that they suffered it at Old Trafford, with two goals from Neymar and one from Marquinhos giving the French champions a rather flattering winning margin.

But United are now in a mess of their own making, which began in Turkey and culminated with Solskjaer's failure to replace Fred at half-time in this game while the score was 1-1, thanks to Rashford's deflected equaliser.

Everyone inside Old Trafford could see that Fred was walking a tightrope from the moment he escaped a red card for pushing his head into the face of Leandro Paredes on 20 minutes. Referee Daniele Orsato reviewed in the incident on the pitchside monitor before deciding only to issue a yellow card to the United midfielder. It was an incredibly lucky escape for Fred, but by half-time, he had also somehow avoided a second yellow following reckless challenges on Marco Verratti and Paredes again.

Any manager, not even an experienced one, would ordinarily withdraw Fred at the interval to avoid the risk of him being sent off.

United have a track record of being hit by costly red cards in Champions League games at Old Trafford. Rafael da Silva (against Bayern Munich in 2010), Nani (Real Madrid 2013) and Paul Pogba (PSG 2019) were all sent off in games that either ended in defeat or elimination for United.

Solskjaer should know that red cards in the Champions League are often punished by ruthless opponents, so he should have replaced Fred with Pogba or Nemanja Matic and protected his team. His subsequent admission that he thought about withdrawing Fred at half-time, before deciding against it, does not do Solskjaer many favours.

"Fred shouldn't put his head towards him [in the first half]," Solskjaer said, when asked about the apparent headbutt on Paredes. "I don't think he touched him. He was a bit lucky to stay on."

So did you think about taking him off?

"Yeah ... Fred has played really well," Solskjaer said. "We spoke about staying calm and on your feet. The second yellow card was nowhere near a foul. Ander [Herrera] knows that."

It is true that, by the time Fred was dismissed on 70 minutes for a careless challenge on Herrera, United had missed two clear chances to take the lead. Anthony Martial missed both of those golden opportunities to score, once again highlighting that he lacks the cold-headed ability of a truly elite striker to hit the back of the net. Had Martial scored either of those second-half chances, United would have gone 2-1 ahead and in a position to kill the game. But the reality was different, with Marquinhos restoring PSG's lead following another failure by United defend a corner properly.

"If Marquinhos had bigger studs on he'd have been offside," Solskjaer said, before adding unconvincingly, "You can't really put your finger on the deciding factors."

The goal was a minute before Fred was sent off, so United's hopes had quite literally gone in 60 seconds.

But this is where the finger of blame points back towards Solskjaer because Fred should have been taken off by that stage. The consequence of him staying on the pitch to be sent off meant United had to play the final 20 minutes with 10 men against one of the best attacking teams in Europe, but it was a self-inflicted wound because Solskjaer should have taken that eventuality out of the equation. The only surprise was that it took PSG another 20 minutes to score again, with Neymar's stoppage-time goal ensuring that the Parisian club now hold the head-to-head advantage over United.

This is not the first time that United have suffered for poor finishing and bad managerial decisions in Europe. They also cast a shadow over Sir Alex Ferguson's Champions League failures. But there is nothing worse than a defeat that has been influenced by your own decisions and Solskjaer, once again, has shown himself to be lacking at the highest level.