Manchester - Kyle Walker has been told by Pep Guardiola he is physically one of the best full-backs in the world, but needs to improve his football brain to maintain his form into his thirties.

The 27-year-old Manchester City full-back has enjoyed an excellent season since arriving from Tottenham Hotspur in July for a fee that could rise to 52 million with performance-related bonus clauses.

Walker has played a key role as City have streaked clear of the of the Premier League field, dropping just two points in their opening 17 matches.

"Right now I'd rate him as one of the best, definitely," said Guardiola of Walker at Friday's press conference.

"He has energy. He is so strong defensively. But I'd like to help him to solve problems not just through his physicality but also through his thinking.

"When you are so strong physically, you solve all the problems that way. When you get to a certain age - 28, 29, 30 - you need to think after that more about what is going to happen.

"I always encourage him to think and after that, do it."

The City manager has revealed that he criticises his players more when they win, because he believes they will be in a better mood to take in what he is saying.

"We try not just to think that if we win, that's good, and it's enough, and if we lose, it's bad," he said.

"That, I think, is a big mistake.

"You have to develop more by talking about the bad things when you win. Because after that, the players don't believe that it's just a complaint or a regret.

"When you lose, you have to work more on their confidence, and say: That is part of the game, you can do better."

Guardiola, meanwhile, has dismissed Manchester United boss Jose Mourinho's claim City commit a lot of 'tactical fouls' to stop opponents counter-attacking.

Mourinho made his comments before last Sunday's Manchester derby, which City won 2-1 at Old Trafford.

"I never, never, never, never sent a message like that to my players," said Guardiola.

"You can ask the players, these players and the old players if my message on the pitch was to commit fouls. I don't use this kind of message."