Manchester United boss Jose Mourinho said it was a “human and professional decision” to allow midfielder Bastian Schweinsteiger to rejoin first-team training this week.
The former Germany captain, 32, has trained alone or with the under-23 side since Mourinho took charge this summer.
Schweinsteiger last played for United in March, under Mourinho’s predecessor Louis van Gaal.
“Schweinsteiger is back,” said Mourinho.
The Portuguese, whose side face Fenerbahce in the Europa League on Thursday, suggested fewer players taking part in training influenced his decision.
He said Schweinsteiger may play for United again despite recent reports suggesting he will leave in the January transfer window.
“If he stays with us he becomes one more option,” said Mourinho. “In this moment we have no problems in midfield like we do in defence.”
Schweinsteiger, a 2014 World Cup winner, was named in United’s Premier League squad for this season, but left out of their Europa League squad.
He has made 31 appearances for the club since his £14.4m move from Bayern Munich in July 2015.
And was a regular member of Louis van Gaal’s side last year when fit, although injuries limited the former Bayern Munich man to just 13 Premier League games.
But he is yet to play a single minute under Mourinho, and is expected to leave the club at the end of the season, if not before.
That is despite the fact that United actually perform far better with him in the side than without.
In the 30 games he has missed since signing, under Van Gaal and Mourinho, United have won only 13 games, or 43 per cent, compared to 10 wins in 18 (56 per cent) without him.