Jose Mourinho has conceded Manchester United are in trouble after Zlatan Ibrahimovic and Marcos Rojo sustained knee injuries.
Both players sustained their injuries in the quarterfinal match against Anderlecht and are expected to be out for the season.
The injury problems is a point of worry for Mourinho, who is also missing Smalling, Mata and Phil Jones.
“We are in trouble,” Mourinho said ahead of Sunday’s trip to Burnley. “We are in trouble.
“In this moment, Eric Bailly played six matches in a row, and we lost Marcos Rojo, we don’t have Jones or Smalling, we are in trouble and now we lose Zlatan too.
“But in attack, we have options and [Wayne] Rooney is coming, and let’s see if Mata can also return before the end of the season, let’s see what happens.”
United are fifth in the Premier League, four points adrift of rivals Manchester City with seven matches remaining.