Schweinsteiger injury doubt
"He has sustained a thigh injury. The doctors say time is running out but we hope he can play because he is an important player," Flick told reporters.
Schweinsteiger has become a leading figure in the team since captain Michael Ballack was injured before the finals and his absence could be costly as Germany seek a quarter-final place.
He was injured late in the 1-0 win over Group D rivals Ghana on Wednesday that clinched top spot.
Midfielder Toni Kroos replace Schweinsteiger, though any decision would be taken closer to the game.
Flick said Jerome Boateng, who started against Ghana in place of left back Holger Badstuber, was also doubtful with a calf injury for the match in Bloemfontein.
Mesut Ozil, who scored the winner against Ghana, twisted his ankle but was fit to play against England, he added.