SHAUN Williams left The Den on crutches and wearing a protective boot last night after hobbling off during Millwall's win over Wigan.
The midfielder slid into an advertising hoarding after losing his footing near the touchline and, despite attempting to play on, was substituted just before half time.
The Lions will assess Williams' problem further – as well as an injury to Shaun Cummings – over the next 24 hours.
Interim boss Neil Harris said: "Shaun walked into the dressing room on crutches, which was a precaution really.
"But anybody who's on crutches after a Tuesday game is going to struggle to play on Saturday [against Cardiff]."
Great result tonight the den was rocking n just to clear it up I slid on the concrete into the wall n didn't kick the boards #COYL
— Shaun Williams (@shaunywilliams6) April 14, 2015
With Williams set to miss the Bluebirds clash and Ed Upson facing a three-match ban for his sending-off, Harris will have to reshuffle his midfield.
"I've got some good players in my squad who can step in," Harris said.
"I had 24 fit first-team players to select from on Tuesday and that's excluding a very good U21 side that is unbeaten in nine games.
"We've got depth at the club and sometimes someone’s misfortune is someone’s gain, and that will be the case for somebody at Cardiff."
Nicky Bailey replaced Williams against the Latics and helped Millwall to a 2-0 victory.
"The game was made for Nicky, as it was against Charlton," said Harris. "In fixtures of this sort, he's a winner and a leader.
"We're so fortunate that if you need to make a sub because of an injury, we've got the likes of Bailey to come on and change the game."