Hammarby chairman Richard von Yxkull told Expressen: "I understand Zlatan was down and training today.
"But there is no major drama in this, he simply wants to keep going and asked if he could train with us. It is so much fun that he wants to train with us."
After taking a fortnight off because of the coronavirus outbreak, Hammarby returned to training this week and have been holding voluntary sessions for players who want to train in a group. This included players from IK Frej, another club.
On Monday, Hammarby will restart training as a group, with the club's manager Jesper Jansson extending the invitation to Ibrahimovic to continue training with them.
Ibrahimovic's decision to become part owner of Hammarby upset supporters at former club Malmo. A statue of the ex-Sweden forward outside Malmo's stadium was vandalised on numerous occasions.
Ibrahimovic has scored four times in 10 appearances since rejoining Milan.