The Eastern European ace only left the Blues in 2011 as a part of a deal for David Luiz after failing to make the grade at Stamford Bridge.
However since being cut loose he has thrived, with regular paying time in Lisbon having seen him emerge as one of European football’s finest holding midfielders.
His fine displays have alerted Mourinho, who is now keen to lure the Serbian back to the club.
‘The Special One’ is looking to inject some physicality into his central ranks between now and the end of the month, and sees the 25-year-old as the ideal man to do so.
Despite having endured a tough time at Chelsea, Matic is said to be ready to return in a bid to prove himself, and could force the switch by requesting a transfer.
The Benfica ace has a £37m buyout clause in his contract, but Mourinho is confident that he can get him for less than that, and is prepared to open the bidding at £21m.
A deal could be part funded by the sale of Kevin De Bruyne, who is closing in on an £18m move to Wolfsburg.