Michael Carrick
An injured Michael Carrick of Manchester United walks along the touchline during Manchester City clash.Getty

Manchester United manager Louis van Gaal says he is hoping Michael Carrick is not injured after the star midfielder was forced to leave the pitch.

The England international limped off in the final few minutes during the Red Devils' 4-2 victory over Manchester City at Old Trafford. The Dutchman had made three substitutions and Carrick was withdrawn as he was struggling from a tight calf.

The former Barcelona and Bayern Munich boss has apologised for using his substitutions too early which left United reduced to 10 men in the closing stages of the clash.

"At the end, Michael Carrick needed to be changed but I could not substitute him. He was very wise to step out of the game with my permission. I hope he is not injured," Van Gaal told United's official website.

Sergio Aguero opened the scoring very early in the game before Ashley Young equalised in the 14th minute for the hosts. United went on to dominate the match after levelling the scores as they scored three more goals.

The Argentine international scored his second goal after Carrick was forced to leave the pitch. Van Gaal claims it was "stupid" not to withdraw the 33-year-old midfielder as he was looking to hand in some playing time for players who had impressed during training.

"We started very badly, we were not the Manchester United we have seen in the last few matches. We were very nervous and I don't know why but we didn't get pressure on the ball at the start," the United manager told Sky Sports.

"Then we scored the goal and from that moment I think there was more confidence in the team and we started to develop our pace and our gameplan. The second half was much better than the first. Until the moment Michael (Carrick) went off we were fantastic."

"That was not so smart. I wanted to give minutes to my players who are working very hard and some players didn't know we were playing with 10 men as we couldn't get the message on. It's very difficult to get the message on with the noise," Van Gaal explained.

United are on a six-match winning streak in the Premier League and this includes victories over Tottenham Hotspur, Liverpool and City. They make a trip to Stamford Bridge as Van Gaal's side take on league leaders Chelsea.

Carrick has been instrumental in the midfield during United's latest impressive run. The former Tottenham player could be doubtful for the clash against Chelsea if he fails to recover from his latest injury. Van Gaal will be hoping the Englishman will be fit to face the Blues.