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Stones has not played for Manchester City since their home defeat by Manchester United on 7 December

Manchester City manager Pep Guardiola says defender John Stones will not fulfil his potential until he stays fit for long periods.

Stones is set to start Saturday's FA Cup tie against League Two Port Vale after recovering from his third thigh injury of the season.

The £47.5m signing from Everton has been restricted to 12 appearances this term.

"To reach the potential he has, John has to play regularly," said Guardiola.

"In the last three and a half seasons he couldn't do it."

Stones has made 121 appearances since he joined City in 2016, Guardiola's debut campaign at the club. That is only 59% of the 205 games the Blues have played since then and evidently, Guardiola thinks the number needs to be higher.

He has not played in successive games since November and it was 12 months prior to that when he last played more than five games in a row.

"He has to be fit," Guardiola said. "After two or three games he fell down and cannot play.

"We tried to help him. We tried to do the best for him since the first day three and a half years ago. We do everything for him.

"It is difficult to know the reason why. Sometimes you have a tough injury but in the case of John, I don't know why he is not able to be a regular for a long period because he is a young player."

Stones' absence has been keenly felt this season as City have struggled with additional central defensive issues following the departure of captain Vincent Kompany and the knee injury that has kept Aymeric Laporte out since August.

It has forced Guardiola to select Fernandinho as a central defender and, for the last three games, play 18-year-old Eric Garcia alongside him.

The City boss still has faith in Stones and doesn't believe the England man's playing career will necessarily be blighted by injury problems.

"He's still young and has his future in front of him," said Guardiola.

"It is in his hands and his head to become one of the best. It depends on him."

Guardiola 'confident' over Fernandinho contract

Fernandinho is one of Manchester City's 'greatest players' - Guardiola

Guardiola says he is confident that makeshift central defender Fernandinho will sign a new contract despite his current deal ending this summer.

The 34-year-old Brazil midfielder has begun talks with City.

He has won three Premier League titles since joining from Shakhtar Donetsk in 2013.

"Of course [I'd like him to stay]. I'm so confident and I'm so delighted with the three and a half years we've had together," Guardiola said.

"He does not have to convince me to stay longer - he convinced me on day one. He knows exactly the opinion we have about what he's done at the club for many years.

"He is one of the greatest players this club has had in its whole history."

Guardiola said Laporte, who has been out since August with a knee injury, is now nearing a return.

"Yesterday was the first time he trained with the team for 10 or 15 minutes," Guardiola said.

"He's getting better, he feels good. I think in the next week he'll complete all the training sessions with us."