Manchester United played out a 1-1 draw with Chelsea at Old Trafford on Sunday.
Juan Mata gave United an early lead before Marcos Alonso scored the equalizer in the 44th minute.
Antonio Rudiger and Willian were substituted due to an injury sustained during the cause of the game.
However, Sarri believes that Willian will play against Frankfurt while Rudiger will not play against Frankfurt on Thursday.
In a post-match interview with Sky Sports, Sarri said:
Willian may only be a knock. He could be back for Frankfurt on Thursday, but Rudiger almost certain to be out.
The blues sit fourth with two points ahead of Arsenal in fifth and three points ahead of Manchester United in sixth.