The Brazilian goalkeeper was forced off at half-time during the 0-0 draw at Sunderland on Tuesday, and Rob Green may again be asked to deputise for Redknapp's first home game in charge of the R's.
Redknapp told the club's website: "Julio looks like he's done a groin.
"We'll send him for a scan on Thursday, once the swelling goes down a bit, and see what the extent of the injury is. We're lucky that we've got two top goalkeepers.
"Cesar has won everything there is to win in the game. He's a top goalkeeper. Rob is an England international keeper and made a fantastic save when he came on.
"He didn't have a lot to do apart from that, but when he was called into action he was fantastic."