Zlatan Ibrahimovic was released by Manchester United in June after his season was ended prematurely by a knee injury, but he is expected to be fit again in December.
"After his contribution last season he deserves our trust and we will be patient waiting for him to return," said boss Jose Mourinho.
Ibrahimovic, who initially joined the Red Devils on free transfer in July 2016, had been recuperating at United's training ground after knee surgery.
Mourinho added: "We are delighted Zlatan is on the road to recovery and we are equally delighted to have his ambition and experience back with us.
"I have no doubt that he will be important in the second part of the season."
Source: tribalfootball.com