The Serbia international quit Stamford Bridge for the second time in his career at the end of last month to reunite with Jose Mourinho at Old Trafford.

And in doing so he brought an end to a successful spell in west London, during which he won two Premier League titles and the League Cup.

Matic faced a battle with Cesc Fabregas and new signing Tiemoue Bakayoko to start alongside N’Golo Kante in Antonio Conte’s midfield this season.

But Le Saux admits he was taken aback by the decision to let the 29-year-old leave Chelsea - particularly for United.

Speaking to Betfair, Le Saux said: "Antonio Conte's comments about the 'crazy transfer market' this summer highlight the lack of depth in the Chelsea squad and I don't see them as obvious champions, particularly with the extra challenge of European football and the fact it's hugely difficult to defend a Premier League title.

"Chelsea have lost John Terry, Nemanja Matic and, probably, Diego Costa.

"Matic, in particular, was an odd sale for me and really surprising that they sold him to a close rival.

"I rate him really highly - he was a brilliant component in the team and gave Conte adaptability."

Chelsea kick off their title defence against Sean Dyche’s Burnley this afternoon.

The Blues won 3-0 when the Clarets came to town last August, but drew the reverse fixture 1-1 at Turf Moor.