Former Manchester United defender Denis Irwin was 'surprised' by Chelsea's decision to allow Nemanja Matic to join Jose Mourinho's side but is happy the Red Devils have signed what he believes to be a 'tremendous' midfield player.

Matic, 29, joined United from Chelsea on a three-year contract in a deal worth £40m (€44.7m, $52.8m) after seemingly being displaced by Tiemoue Bakayoko at Stamford Bridge, but many have questioned the Premier League champions' logic to strengthen a perceived rival for their crown.

Irwin, who spent 12 successful seasons at Manchester United between 1990 and 2002, admits he was taken aback by the arrival of Matic at Old Trafford and suggested that Chelsea's decision to let Serbia international join United was a way of saying thank you for his service during his three-and-a-half year spell in west London, during which the Blues won two Premier League titles.

"I was a little bit surprised by the fact Chelsea are selling to their rivals who will be challenging for the Premier league next year," Irwin told talkSPORT. "But Matic has done a fantastic job for Chelsea over the last few years and I suppose it was a bit of a thank you [to let him join Manchester United].

"Manchester United have got a tremendous player, a tremendous holding player, and they've needed somebody of that ilk. I think it's a very good signing."

Mourinho has signed a number of strong, towering players since arriving at Manchester United last summer, and Irwin has been impressed with the Portuguese's recruitment. The former Chelsea boss has signed seven players over three transfer windows, and Irwin thinks the signings, combined with improvement from others, will spark United's title charge.

"Since Jose has come to the club, the seven players they've signed a lot of them are tall, physical players – players you need for the Premier League. There's a good mixture of youth and experience too.

"Lukaku is a 25 goals-a-season striker, I expect Marcus [Rashford] to even better this year and I see [Henrikh] Mkhitaryan improving a lot as well, so I expect to see more goals. I expect them to challenge [for the title] this year."

The arrival of Matic seemingly has no impact on the future of Marouane Fellaini in the eyes of Mourinho, but the Belgium international is reportedly considering his future at Old Trafford.

Galatasaray were believed to be close to signing the former Everton star, who had supposedly agreed a deal worth €4m-a-season with the Turkish giants, but the 29-year-old is now prepared to wait until January in order to see where the land lies in Manchester.

Marouane Fellaini and Nemanja Matic
Matic's arrival came as a bit of surprise to Irwin. Getty Images