The England left-back has not played for the Red Devils' first team since he suffered a foot injury against Swansea City in April.
However, Shaw has started the last three matches for the club's second string against Leicester City, Tottenham Hotspur and Arsenal, and could feature again in their trip to Chelsea on Monday night.
Despite now reportedly with the senior squad again, Shaw was not included in the squad for Tuesday night's Champions League win over Basel, and Mourinho has suggested that his return to the first team could depend on his form in the reserves.
The Portuguese coach told reporters on Friday: "Luke Shaw is not injured any more so it is a question of form. It's a question of option but he is not injured, he's recovered from his injury."
Shaw has made 47 appearances for Man United since his 2014 switch from Southampton.