Swansea boss Paul Clement has expressed his surprise that Chelsea allowed Nemanja Matic to join Manchester United as he prepares for a reunion with the player.
Clement worked with Matic during his time as Carlo Ancelotti's assistant at Stamford Bridge before the holding midfielder joined Benfica in 2011.
Matic returned to Stamford Bridge two-and-a-half years later and was a driving force as Chelsea won two Premier League titles in three seasons.
But Chelsea sanctioned Matic's B#40million transfer to Old Trafford last month - and the 29-year-old Serbia international made an impressive start to his United career with a man-of-the-match performance in the 4-0 season-opening victory over West Ham.
"I was surprised Chelsea let him go, I don't know how that deal managed to happen," head coach Clement said ahead of United's visit to the Liberty Stadium.
"It's not too good for Chelsea and Antonio Conte has made it clear he did not want that to happen. It is a win for United.
"He is good positionally, he has good physical stature, he is strong in the challenge and good in the air.
"He has also a nice left foot and is an under-rated passer and is very focused on his football."
Matic made only three senior appearances for Chelsea under Ancelotti, all as a substitute, before spending the 2010-11 season on loan at Dutch club Vitesse Arnhem.
"I was not sure about him when I worked with him, and I don't think Carlo was because he did not play much," Clement said.
"But at that time Chelsea had a really strong midfield - John Obi Mikel, Michael Essien, Frank Lampard and Michael Ballack.
"So it was always going to be hard for him to break in and the club decided to sell him to Benfica.
"But he did really well and they got him back in the end."
Ahead of the game, Jose Mourinho accepts Manchester United are now unlikely to sign the wide man he had hoped for this summer.
Hard work behind the scenes has seen the Reds' squad bolstered, with defender Victor Lindelof and striker Romelu Lukaku both arriving before the pre-season tour of the United States got under way.
With Matic also, last week Mourinho was still hoping executive vice-chairman Ed Woodward would be able to complete the last "25 per cent" of business.
The Portuguese spoke of his desire for "somebody playing from the sides", with Inter Milan's Ivan Perisic trailed and Tottenham's Danny Rose and Real Madrid star Gareth Bale linked over recent weeks.
However, Mourinho has now accepted that a fourth acquisition is probably out of their reach.
"I don't think we are unless something happened that puts us in the market again," the United boss said.
"I told Mr Woodward that obviously my plans were four, but I also told be cool, no pressure from me, do what you think is the best for the club.
"We will be together again for another transfer window in January and another one in the next summer, so there is no pressure from me at all and I am happy with the squad we have.
"I am ready to go without the fourth player, so if we are out of the market I am fine. I'm ready."