Diego Costa will face Manchester City on Sunday despite Jose Mourinho admitting the Chelsea striker needs rest to clear up a hamstring problem.

Mourinho revealed this week the forward started Wednesday's Champions League clash with Schalke on the bench because Costa's condition means he is unable to play more than once a week.

But the striker -- who suffered the injury during the recent international break with Spain -- will return to the starting line-up at the Etihad Stadium as Chelsea seek to extend their perfect start to the Premier League season with a fifth successive win.

Costa has scored seven goals in four Premier League games following his is £32 million ($53.1 million) pre-season move from Atletico Madrid, highlighting why Chelsea manager Mourinho is so keen for the forward to start against City.

Mourinho, though, conceded Costa's starting appearance against Premier League champions will mean he is unable to face Bolton in next week's League Cup clash.

"Diego is not in the best conditions, but he will start the game," Mourinho told reporters at Chelsea's Cobham training ground, south of London, on Friday.

"He plays this game, he cannot play against Bolton. It's as simple as that."

When asked if the player would benefit from two weeks complete rest, Portuguese boss Mourinho added: "Yes."

Mourinho explained Chelsea will have to manage the striker's condition carefully.

"The player is amazing, his attitude is amazing. Clearly, we have to try and protect him until he gets completely fit.

"He plays Sunday, doesn't play against Bolton. He plays against Aston Villa on Saturday. At this moment, decision made. Let's see his evolution and let's hope he goes in the right direction and becomes available to play every game."

Mourinho and his players face the prospect of a reunion this weekend with Frank Lampard, who unexpectedly joined City on loan from New York City before the start of the season.

Lampard agreed terms with the United States club after leaving Chelsea as a free agent at the end of last season following a 13-year stay at Stamford Bridge before making a temporary switch to City ahead of the 2015 Major League Soccer season.

Mourinho said he never expected to face Lampard in these circumstances after the 36-year-old midfielder left Chelsea.

"It's football. If you'd said that four or five years ago, I would have said it was strange," said Mourinho.

"Even a few months ago, when he signed for the New York team, I was not expecting this. But it was his decision. It's life.

"When he left for New York, I thought he was going there. But it's his life, his decision, and he has my respect for that."

Last season, Mourinho played down Chelsea's strengths in comparison to City after beating Manuel Pellegrini's side in the corresponding fixture in February.

But the manager accepted Chelsea are a much stronger team this time around.

"I don't want to compare," Mourinho said. "I just want to say that I feel our squad is better than last season.

"We have more solutions. We got a couple of players with qualities which we didn't have last season. We feel that, with our squad, even in a short squad of 21 players, we have a good balance, a good squad and we're happy with that."