It had looked like the 32-year-old midfielder would never play for United again having been frozen out by the Portuguese after succeeding Louis van Gaal.
Schweinsteiger's stock plummeted so far that United even had to write him off as an asset in the club accounts given he was "no longer considered to be a member of the first-team playing squad".
It was therefore quite a surprise to see the former Germany captain training with the first team on Monday, featuring prominently in a series of images shared by the club
The decision has been widely welcomed, with Mourinho highlighting squad preparation as key as well as the chance for Schweinsteiger to build fitness should he decide to depart
"Schweinsteiger is back," Mourinho said
"We made that decision last Thursday and informed him on Friday, so he would join the team on Monday.
"It's a decision based on the fact that we are in a period in the season where it's really difficult to train with everybody together.
"So the problem of tactical work like I do with 21 players, 23-24 max, that doesn't happen because the day after we play the players that played train in a separate group so the group becomes 13 or 14.
"Then with injuries sometimes it becomes 10 and 11
Many times we go to the academy to bring some young boys to have a group with the perfect numbers to train.
"This is happening now match after match, week after week
For example, on Friday the players who played here will not train with main group.
"Looking at Bastian and the way he was working professionally every day with a fitness coach, we think it's a human decision, it's a professional decision to bring him back to the team.
"He will be much better prepared, he will be in much better conditions in case his future decision to leave the club, he will be prepared to go direct to competition.
"If he stays with us, he becomes one more option
In this moment we have no problems in midfield like we do in defence but if we do he is one more option for us.
"So it's a human decision based on the training numbers and the training methods, but it's also a decision that can be positive for the group
A good decision for us, a good decision for him."
The United midfield looks bloated in terms of options right now, but the same cannot be said for the backline.
A foot complaint has kept Chris Smalling out of the Europa League clash with Fenerbahce, meaning he joins Eric Bailly and Antonio Valencia on the sidelines.
The former faces two months out and the latter a reported six weeks, with Mourinho only saying the right-back will "be out for a while" after undergoing surgery on a fractured arm.
Such paucity of defensive options means Phil Jones has been rushed back into the fold having just recovered from a knee issue.
The oft-injured defender last played a competitive match 10 months ago, but could be involved in United's Group A game against Fenerbahce on Thursday.
"Well, I almost don't remember when Phil Jones had a good run of matches for United," Mourinho said
"I don't remember.
"I remember that when I was at Real Madrid in maybe 2012 I played against Man United and Phil Jones played in Madrid for Man United
I don't remember many occasions after that where Phil was ready.
"He's having a difficult relationship with injuries
It's been a difficult period for him, but he worked hard to recover and is training with the team for more than a week now.
"We are in a difficult situation because we lost three defenders in a week - Valencia, Bailly and Smalling - and because we are in a difficult situation we don't have more time to be in better conditions, so we have to select him and maybe we have to play him."
Michael Carrick and Memphis Depay have remained in the north west, but Henrikh Mkhitaryan, Anthony Martial and Tim Fosu-Mensah are part of the 21-man squad in Turkey.
Source : PA
Source: PA