Ibrahimovic was soon released by the Red Devils at the end of the season, but United offered a generous gesture by providing him complete access to the club's training facilities.
Ibrahimovic played a major role in Manchester United's success last season, scoring 28 goals as the club won the EFL Cup and Europa League - returning to the Champions League as a result.
Mourinho believes United are capable of winning a title in his second season, but is not kidding himself over the challenge that awaits them domestically.
Ibrahimovic's contract at Old Trafford came to an end at the end of last season, and he is now a free agent. From the physical side of it, I think La Liga is not the Premier League in terms of the physicality. It's not something that's urgent, it's not desperate to have it done or not.
"I just think he was very clear showing what he did last year was not enough for him".
"He wants more at football's highest level, so we are having conversations and we are discussing the possibility of him staying with us for the second part of the season".
"My teams always had the goalscorer - the guy that scores more goals - but then we had the winger that scored 15 goals, the midfield player that scored 10 goals and we had the central defender that scored five goals".
United kick off their Premier League campaign at home to West Ham on Sunday, having won six of their seven pre-season friendlies.
That's different to the three other leagues [Portugal, Italy and Spain] I have worked in.
"Victor can play right-back and can play centre midfield, we got a centre midfielder and we got an attacking player", he said.
"I hope he doesn't leave Madrid". Can he still contribute to the team after his serious injury?