The Serbian has spoken about his love for football and was in attendance as Milan faced their inner-city rivals Inter Milan in the first leg of their Champions League semi-final.
And his appearance at the San Siro among former Milan legends has sparked suggestions that the 35-year-old favours the Rossoneri over Manchester United or Real Madrid.
Is Djokovic an AC Milan fan?
Djokovic has made it clear throughout his career that tennis comes first, but football isn't far behind.
He's been spotted in Real Madrid gear before while he has praised Manchester United and claimed he supports the Red Devils. However, there is a huge body of evidence to suggest the Serb is a Milan fan.
In 2014, he was quoted as saying: "I'm a big fan of Milan and I'll always be. For me, football is second only [to] tennis. My father was a professional footballer, and at home, we always watch the Rossoneri's games with great interest."
And last year, before the Rossoneri won Serie A, he revealed he was good friends with Zlatan Ibrahimovic and had exchanged messages over Milan's title charge.
Djokovic said: "I am friends with Zlatan Ibrahimovic. We often talked about my situation in Australia. He also supported me publicly, which I really appreciate. I'm a Milan fan and we hope to win the Scudetto this year."
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Once Milan won the Scudetto, Djokovic posted a message on his Instagram congratulating the team.
This was followed by a clip from September 2022 that appeared to show Djokovic chanting a song about Milan's boss Stefano Pioli.
The footage is unclear but the official AC Milan Twitter account responded to the clip, suggesting it's genuine.
So though Djokovic has spoken about Man United, it is pretty clear that the tennis star is an AC Milan fan.