The defender appeared to turn over his left ankle and was forced out of the action in the 65th minute of Saturday's Premier League encounter at the Lane.
He was replaced by Ben Davies, who slotted in seamlessly into the left-side of our three at the back system, a position and system he's familiar with on international duty with Wales.
Jan had to be helped back down the tunnel and Mauricio reported that he will be assessed on Sunday and Monday.
"We all feel very sad about Jan, it’s disappointed us a lot because it was bad luck in the way that he had the injury," said Mauricio.
"We need to wait and hope it’s not as bad as we believe. We will assess him tomorrow and Monday but be sure that we will help him, look after him and try to push him to be available as soon as possible."