LOS ANGELES -- Manchester United manager Erik ten Hag says he wants to boost the depth of his squad ahead of the new season.

United have signed Leny Yoro and Joshua Zirkzee to replace departed pair Raphaël Varane and Anthony Martial.

And while Ten Hag refused to put a number on the new signings he would like before the transfer deadline, he admitted the club are playing "catch up" with regards to the depth of the squad.

"We need the squad to be as strong as possible," Ten Hag said at a news conference at UCLA on Friday.

"We already had a very good two buys, so when everyone is fit we have a team who can beat everyone, but with the squad depth we have to catch up because we had injuries, we are vulnerable.

"We have to avoid this by getting less injuries and second, our squad has to be that good. The quality we have in depth we have to catch up, but even more because this season will be the survival of the fittest."

Sources have told ESPN that United are particularly focusing on centre-backs, central midfielders and full-backs.

Left-back is an area of concern with Tyrell Malacia still not fit after a year on the sidelines with there are doubts about the future of midfielder Casemiro.

"We are looking in all of the positions to reinforce and we are looking for a plan in our squad to reassure ourselves we are always occupied," said Ten Hag.

"We work continually and the good thing is we already signed two players and it belongs to a club like Man United that you are looking for opportunities that are better and we still have time until [the deadline on] Aug. 30.

"The load and pressure on players is immense, with the new model in Europe. I just mentioned it, it's survival of the fittest."

Ten Hag is taking charge of his third preseason tour as United manager after minority owner Sir Jim Ratcliffe and his team made the decision to stick with the Dutchman.

He had to endure a nervous three-week wait following the FA Cup before learning he would stay, but Ten Hag insists it's time to move on after the uncertainty.

"We are now in a new season, we left everything behind, we are looking forward, it's a great project," said Ten Hag.

"The process is nice, we go with ups and downs and now we are very energised, good dynamic, good spirit, looking forward, we want to work and we want to win.

"I never think if I'm in a strong position or weak position. I want to collaborate. I can't do this on my own, players, staff, leadership, everyone. I'm sure we will have even more success."

Meanwhile, United have appointed Andreas Georgson as a first-team coach.

He comes in from Lillestrom, where he was head coach, and has worked at Brentford, Arsenal and Southampton. The 42-year-old will have a focus on set pieces.