Diaz made the difference in the first leg as his goal meant AC Milan head into the second leg with a 1-0 lead over Tottenham.
The on-loan Real Madrid midfielder also has four goals and two assists in Serie A this season, but he could be unavailable for the return leg against Tottenham.
Pioli revealed that Diaz has endured a knee sprain and thus will miss the league game this weekend against Fiorentina, while Charles De Ketelaere will take his place.
“Slight knee sprain for Brahim Diaz, De Ketelaere will play tomorrow”, Pioli said in a press conference ahead of the Fiorentina game.
The AC Milan boss insisted that the club will try everything in their power to make sure the attacker is ready for the Tottenham game.
“We will do everything to get him back for Tottenham”, Pioli added.
Tottenham will be looking to overcome the 1-0 deficit in the second leg and advance to the quarter-finals for the first time since the 2018/19 season.
