Ibrahimovic joined Milan for a second time in December 2019
Zlatan Ibrahimovic is to be investigated by Uefa over an "alleged financial interest in a betting company".
According to reports in his native Sweden, the AC Milan striker, 39, has broken rules after becoming a partner in a betting company.
Uefa's disciplinary regulations state players should not have a financial interest in betting.
Last week he signed a new contract that will run until after his 40th birthday.
"A Uefa ethics and disciplinary inspector has today been appointed to conduct a disciplinary investigation regarding a potential violation of the Uefa disciplinary regulations by Mr Zlatan Ibrahimovic for having an alleged financial interest in a betting company," a Uefa statement said.
The former Manchester United striker has scored 17 goals in 25 appearances in all competitions this season.
Ibrahimovic came out of international retirement after a five-year absence to play for Sweden earlier this year.
Meanwhile, Ibrahimovic has been fined 4,000 euros (£3,500) for his part in an ugly clash with Inter Milan striker Romelu Lukaku during a Coppa Italia match in January.
The pair were involved in a number of exchanges and Ibrahimovic, who denied he used racist language, was eventually sent off.
Like Ibrahimovic, Lukaku was charged with "unsportsmanlike behaviour with provocative phrases" by the Italian Football Federation. The Belgian has been fined 3,000 euros (£2,600).