The 27-year-old was taken injured in the 75th minute of the R's 2-1 victory over Derby County at Loftus Road this afternoon, with the midfielder's reaction to the injury prompting fears over its seriousness.
The club have confirmed that the Argentine will undergo a scan on Monday in a bid to determine the extent of the damage, but Redknapp has revealed that he is pessimistic about the results.
"It doesn't look good," he told the club's official website. "It's his left knee. Everyone's keeping everything crossed that it's not as bad as we fear."
The West London outfit, who remain within two points of Championship leaders Burnley, had not won in their previous three outings in England's second tier prior to the visit of the Rams.
However, the former Tottenham Hotspur boss is pleased about the energy surrounding the team's promotion bid - both on and off the field.
"We've had three difficult away games. We've come back against a tough Derby team and we deserved the win," Redknapp added.
"I like the look of us. We're playing well and the atmosphere around the place is just fantastic."
Derby's Simon Dawkins cancelled out Jermaine Jenas's 11th-minute opener, before an own goal from Jake Buxton saw the Londoners claim all three points.
QPR travel to Reading in the Championship next Saturday.