COUNTY KILDARE, Ireland -- Michael Carrick has admitted Kobbie Mainoo's World Cup experience was "challenging," but insisted the tournament was still a positive experience for the Manchester United midfielder.
Mainoo didn't play a single minute for England before picking up an injury which ruled him out of the third-place play-off against France.
Carrick faced a similar situation when he failed to make an appearance at the 2010 World Cup. The United head coach said the experience helped him "support" Mainoo throughout a difficult summer.
"I spoke to him, I spoke to him all the way through the World Cup, little bits, not loads, but little bits," Carrick said. "It's challenging, we all see from the outside the glitz, the glamour, all the positive side of football and players are human beings and we all have our ups and downs, so it's important that we support each other.
"It was a good experience for Kobbie to go there and it's a World Cup, so that step to be there is a big step. He's still such a young man and he's achieved so much so far, so quickly, that to be at the stage he's at is an achievement in its own right, but yeah, for sure it's frustrating when you want to play and you want to have an impact.
"That in itself, if you're not, has its own challenges, but he's come back, he's been in great spirits this week and it's nice for him to be home and looking forward to the new season."
Thomas Tuchel has faced criticism for his decision to keep Mainoo on the bench at the World Cup.
But Carrick stopped short of adding his voice and said his only focus is to ensure the youngster is ready to start the season with United when it kicks off against newly-promoted Hull City on Aug. 22.
"Everyone's got their opinion," Carrick said. "There's a whole squad of good players, that's why it's the World Cup and it's England, so it's not for me to [criticise].
"The biggest thing for me, Kobbie's in a really good place. I think he feels that. He's come back and he's come home and he's ready for a big season, and seeing him this week, it's been great to have him back."
Mainoo rejoined the United squad at their training camp in Ireland along with England teammate Marcus Rashford.
Rashford is back after spending 18 months on loan at Aston Villa and Barcelona after the Spanish side chose not to make the move permanent.
Speaking in an interview at United's team hotel, Carrick refused to be drawn on whether the 28-year-old will definitely be part of the squad this season, although he said the return of the academy graduate -- who has two years left on his contract at Old Trafford -- has the potential to be exciting.
"He's our player," Carrick said. "I've known him a long time, like I've known some of the others a long time, so I don't treat him any different to anybody else, but it's been good to have him around the group again this week. So I'm really positive with that.
"He's a very good player, Marcus, and I think if you're going to have a career over 10 or 15 years, there's going to be times when things go in a direction and maybe a different direction.
"I think there's ups and downs, and that doesn't judge you as a one-off kind of judgment. It's what happens over time, and now we're in a positive place as a group, and Marcus can offer us so much. He has done, and he can do again, so in that respect, it's quite exciting."
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As well as Rashford's return, United have also added Youri Tielemans and Andrey Santos in the transfer window.
Carrick has said the club "need" more signings before the deadline. But even with the squad as it is now, he believes United are set up for a successful season.
"We've definitely got the potential to achieve something really special," he said. "I'm not hiding from the fact, and we should aim to do that, but I can't give you a definite answer [on whether United are title challengers]. It's certainly what we're pushing to do because we have to, because that's the club we are."