Ulf Karlsson, who was head coach of Sweden's athletics team between 2001 and 2004, claimed last year that Ibrahimovic must have used performance-enhancing substances in order to build muscle mass.
"Zlatan gained 10 kilos of muscle in six months at Juventus. That is impossible in such a short time," he said in a panel discussion, before adding to newspaper Nya Wermlands-Tidning: "I think he was doped. I am convinced."
He has now been fined 24,000 kronor ($3,691) after a Swedish court ruled that his comments amounted to slander.
"Even if his remarks do not contain a direct accusation that Zlatan Ibrahimovic had taken steroids, the court finds that these remarks, given the context in which they were made, cannot be taken any other way than to give the impression that Zlatan Ibrahimovic would have taken steroids during his time at Juventus," the court's verdict read.
Karlsson was acquitted over the remark made to Nya Wermlands-Tidning, however - a decision welcomed by his legal team.
"I'm glad the district court has agreed with me that he should not be convicted for what he has said to a journalist. That's an important principle," attorney Johan Eriksson said.
Ibrahimovic joined Juve from Ajax in 2004 and spent two years in Turin. He left to join Inter after Juve were relegated to Serie B following the Calciopoli scandal.