Both Costa and Matic have always been touted with a move this summer after being considered surplus to requirements by Conte, with Atletico Madrid and Juventus the front-runners for the duo respectively.
Three years later, the Serbia worldwide, at the request of Mourinho, who else, was back at the Bridge - but it cost Abramovich £21m to sign Matic as there was no cordial buy-back clause in his sale contract.
It is understood that Conte is already anxious that Bakayoko may not be ready to start for Chelsea until September, meaning he would miss the first three Premier League games of the season against Burnley, Tottenham Hotspur and Everton.
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Selling Matic to Juventus would likely be a more acceptable option for Chelsea than the midfielder joining Premier League rivals.
Tiemoue Bakayoko has trolled Chelsea fans ahead of his move.
The 18-year-old forward has been linked with Spanish and European champions Real Madrid, as well as Arsenal, Manchester United and Barcelona.
Italian publication Corriere dello Sport have reported that Inter Milan have emerged as suitors for Nemanja Matic.
The 22-year-old Bakayoko was pivotal in helping Monaco win the French league last season and Chelsea had been sounding out the playmaker about a move to west London.