​Nemanja Matic has explained why Jose Mourinho was the key reason behind his £40m switch from Chelsea to Premier League title rivals Manchester United.

The midfield enforcer spoke exclusively to ​Sky Sports about his surprise transfer to Old Trafford ahead of his side's clash with Swansea City on Saturday.

Matic had worked alongside Mourinho during the pair's time together at Stamford Bridge and, with the duo enjoying a good working relationship, the 29-year-old revealed that he didn't have to think twice about being reunited with the Portuguese gaffer in the north west.

Manchester United v West Ham United - Premier League

He said: "He [Mourinho] was very important for me. He bought me to Chelsea from Benfica and now when I decided to come to Manchester, he was a reason to come here.

"Mourinho was the reason and so was the club, Manchester United, so you don't need to think a lot about if you are going to come. My decision was very quick and very clear."

Matic has already drawn praise for the manner of his performances in an United shirt, and the Serbia international clearly revelled in his league debut for the Europa League holders in last weekend's 4-0 thumping of West Ham.

Asked whether he considered his new club to be a bigger team than Chelsea were, Matic was unequivocal in his response.

He stated: "Definitely, everyone knows what Manchester United is about. When you say Manchester United, it is different. Also Chelsea is a big club, Benfica are the biggest club in Portugal. But Manchester is Manchester.

"When I came here for the first day, I could feel that the people at the club help you every day if you need something and supporters are very important for this club.

"After every training session, they are waiting for us outside the training ground to take pictures, to give a signature so I think the club is one of the biggest in the world.

"Maybe you have two or three clubs similar to United, but Manchester is one of the biggest clubs in the world for sure."

Matic was given a greater license to roam forward during that triumph over the Hammers last Saturday, and the ex-Benfica star added that he would try to get "forward and score some more goals" if given the chance to do so.

He said: "I've played as a defensive midfielder for many years so I will try to continue to do my job the best that I can. I will do my best but when I have the opportunity to do something more or to go up front, I will do it but supporters and my team-mates know my job is to give balance to the team, to defend well and I will try to do the same job like I did before. I think I can still improve and I will do it of course."