Mourinho was sacked by the Blues back in December 2015 after his second spell at Chelsea ended on a sour note.
The Portuguese coach was dismissed with his team closer to the bottom of the table than the top, just months after he led them to a League Cup and Premier League double.
Chelsea moved quickly to bring in Antonio Conte as their new manager last summer and the Italian has had a superb impact at Stamford Bridge.
The Blues have been the Premier League’s top performing team this season and are currently seven points clear at the top of the table heading into Sunday’s crunch clash at Manchester United.
And Mourinho has lifted the lid on what he really thinks about Chelsea under Conte this season.
Mourinho told BT Sport: “First of all, some guys are fresh, some guys are tired. That’s very important in football.
“But, for some reason, they are top of the league. It’s not just because they are fresh. It’s also because they have individual quality and they have collective quality.
“They have a certain style of play, they stick to it, they do it very well. Not every team defends with 11 players, and they defend with 11 players.”
Manchester United are fifth heading into this weekend’s round of games.
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