The Portuguese superstar has signed a new deal with the Rossoneri but had to watch from the sidelines as his side fell to a 2-0 defeat at the San Siro.
But after being withdrawn against Lazio earlier this month with a muscle problem, will Milan's star forward be fit to face Inter in the crucial second leg?
Will Leao be fit for the second leg of the Champions League semi-final?
The 23-year-old has been Milan's best player in their run to the last four of UEFA's premier club competition.
The forward has scored one goal and set up a further five, including two in the quarter-finals against Napoli.
He has been a crucial cog, and Stefano Pioli's side really felt his absence as they struggled to offer much attacking threat in the biggest game of their season.
Leao was forced to watch from the stands as his team wilted under pressure, and it's unclear if he will be fit for the return leg next week. The former Lille man started in Milan's last Serie A game against Lazio but only lasted 11 minutes before he was withdrawn with a thigh problem.
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Ahead of the Inter match, Pioli revealed that Leao would either start or miss out completely and wouldn't be used from the bench.
Leao spent the night with the Milan side at their hotel and underwent scans ahead of the first leg, but it was deemed too risky for him to play.
We now await an update from Pioli or elsewhere ahead of the second leg between the two Milan giants.
However, as it stands, Leao's involvement in the next leg of the Champions League semi-final looks doubtful at best.