London - John Stones faces a battle to win back his place at Manchester City after manager Pep Guardiola expressed reservations about his ability to deal with high balls and powerful opponents.
City paid 47.5 million ($59.6 million, 55.7 million euros) to sign Stones, 22, from Everton in August, but after some error-strewn displays, he has started their last two matches on the bench.
Speaking after City's 3-0 FA Cup win at Crystal Palace on Saturday, Guardiola also suggested Stones, Nicolas Otamendi and Vincent Kompany are competing to partner converted left-back Aleksandar Kolarov.
Asked what Stones needs to do to earn a starting berth, Guardiola told reporters at Selhurst Park: "Fight like he fought in the beginning of the season.
"If you see my line-ups for the last three, four, five months, I try to have all the players play. I try. So he's played a lot.
"But now, for this kind of stadium, for (Christian) Benteke, for the long balls, I decide to play two central defenders more strong in the air (Kompany and Kolarov).
"I will continue to play a left-footed central defender on the left side, like Kolarov. But I remember the last games he played, especially in Anfield, even in Goodison Park, they played good."
Kompany, the City captain, made an assured return to action after recovering from a knee injury sustained during his side's 2-1 win at the same ground in November.
Guardiola praised City's medical staff for their work with the injury-prone Belgium international, saying they were "some of the best I ever worked with in my life".
But he said he was unsure whether Kompany, 30, would be able to keep his place in the starting XI for Wednesday's trip to West Ham United in the Premier League.
"We are going to see (on Sunday) the regeneration and after then we will see," Guardiola said.
"It depends on his physical condition. Of course he's an important player, but I always believe that how many chances created, how many chances conceded, does not depend on just one player.
"But of course what we want, what I want as manager, is not (just) using him, but for himself.
"They are football players, they are professionals. When they are out for a long time it's a disaster for them, mentally so tough.
"In that case he played 90 minutes and now we are going to see what's going to happen."
Also read: City splash out on Everton's Stones
- 'Looking for bad luck' -
Kompany has suffered 35 separate injuries since joining City from Hamburg in 2008, a period during which he has notably contributed to two Premier League title wins.
Despite having spent over two months on the sidelines, he said he had prepared himself mentally for the challenge of plunging back into action.
"I want to play, but at the same time I'm a fighter," Kompany told reporters.
"I will not give up -- it's impossible for me. I've always been confident I can come back and do a job.
"Most players have six weeks of pre-season and loads of games against lesser opposition, but I've not had any of that.
"All of these games are my first games, but I know I have to deal with it, know I have to handle it.
"I know I've not got the time to say to the guys, 'Hold on, I know in three or four games my performances will be better.' Experience helps a lot and I'm always confident I can do a job."
He also said he had had no qualms about returning to the scene of his most recent injury.
"I don't think like the usual person," Kompany said.
"For me it makes more sense -- if something brings me bad luck, I'll go looking for it again to see if it'll be bad luck again. That's how I am."