Chelsea's players have made uncharacteristic errors in recent weeks - allowing a 3-1 lead to slip against Tottenham and then gifting Fenerbahce victory in Turkey on Wednesday after leading 1-0.

German midfielder Michael Ballack has already voiced his concern over Chelsea's mental fragility and Grant admits their aberrations always seem to happen when the team is playing well.

"It has happened to us for the second or third time and especially when we play well," he conceded.

"We lost our concentration against Tottenham in what was one of our best performances in the league. It then happened in the Champions League when we produced one of our best performances in Europe.

"When you play well, maybe it is human nature, you think everything is going well and you don't need to be careful.

"This is why people like football, this is also the reason I didn't like the game on Wednesday.

"We don't like it and it will not happen again. We need to continue to play good football like we did against Tottenham and Fenerbahce but we need to concentrate all the game. One attack can lose you a game like it did on Wednesday."

Chelsea travel to face Manchester City tomorrow and that provides them with a golden opportunity to put some pressure on leaders Manchester United, who play Middlesbrough on Sunday.

Grant added: "We are coming now to the important part of the season and we need to do our job.

"Manchester United are ahead of us and they have tough games like us. We need to do our business and maybe put a little bit of pressure on them.

"It is an opportunity we must take after winning so many games and winning against Arsenal, we need to do everything to win games and pass one more team.

"You cannot only think about the next game because there is a lot of physical and mental pressure. We have a game every three days now so we first think about tomorrow's game and have one eye on the return leg of the semi-final.

"We are six games from the end and we want to face Manchester United here at Stamford Bridge in a good position and to do that we want to win the game tomorrow.

"It is an important game against Manchester City and we need to win it.

"In the last two or three months we have played very good football. Sometimes you cannot play well all the time.

"On Wednesday, it was one of our best performances in Europe but while I accept the last 15 minutes against Middlesbrough (in last weekend's 1-0 win) were not good, we won the game."

Grant is set to rest some of his top players ahead of Tuesday's return Champions League quarter-final match against the Turks.

Nicolas Anelka is likely to lead the attack with Didier Drogba rested and Carlo Cudicini is set to remain in goal despite Petr Cech's ever-improving rehabilitation from an ankle problem.

Grant said: "Until yesterday Cech had made a lot of improvement and we need to see where he is at the end of the recovery period.

"He is better than 50-50, he is almost ready. It will be a medical decision. But we have other goalkeepers who have done a good job this year."

Grant also played down suggestions of a rift between him and England midfielder Frank Lampard.

The player was unhappy when substituted against Fenerbahce but Grant insists there is no problem between the pair.

"Frank is a very passionate player," said Grant. "He was very disappointed that Fenerbahce had equalised.

"I shook hands with Frank. I like passionate players. If his reaction was good or not, it is an internal matter.

"The discipline at Chelsea has been very good since I've been here. I speak with all the players, but I speak about the game and not something else.

"Everybody was disappointed. It was one of our best performances but we lost the game so he wanted to understand why, that's all."