David Luiz was forced out of Chelsea's Premier League game against Aston Villa on Saturday, during first half stoppage time. The injury was bad enough that he wasn't able to simply finish the half and make a decision about his status in the locker room, and he was replaced by Gary Cahill. He appears to have injured ankle ligaments, and he'll likely learn more about his status on Monday.
The good news for Chelsea is that Gary Cahill has been in good form and that there shouldn't be too much of a drop-off if David Luiz has to miss time, but it will leave the Blues dangerously thin at the back. It's also a terrible time for the Brazilian to go down. Not only because Chelsea might need to win every one of their remaining games to finish in fourth place, but because David Luiz has recently cut down on his mistakes at the back and has been much more consistent under Roberto Di Matteo than he was under Andre Villas-Boas.
Chelsea are also awaiting an update on the status of Didier Drogba, who picked up what appears to be a minor foot injury in warmups.
For more on the Luiz and Drogba injuries, head over to Chelsea blog We Ain't Got No History.