“He (Austin) failed a medical at Hull a couple of years ago," Sullivan said in the KUMB interview. "They say he has no ligaments in his knee, who knows? To sign a player for £15m is a big risk.”
Sullivan has since gone on to clarify his comments about the 26-year-old, telling KUMB: “I fully accept that day to day he is fine and that his recent form is fantastic. The question is whether past injuries will impact on the longevity of his career.”
Former QPR manager Redknapp has now given his take on the matter, claiming that Austin has no problem whatsoever with his knee.
“I never knew Charlie Austin miss one day’s training, let alone a match,” the former West Ham and Tottenham Hotspur boss wrote on Kicca.com. “Every single day he was on the training pitch.
“For whatever reason he failed a medical but Charlie doesn’t miss training, doesn’t miss a game. He’s got no problem with his knee, he doesn’t have to sit there with ice on his knee all day, every day he’s out on that training ground.
“He’s 100 per cent fit, and anybody interested in Charlie shouldn’t be worried, I’d back him all day long, his fitness record is not a problem.”
Austin was one of the best players in the Premier League last season and arguably the best for QPR.
The Englishman did all he could to prevent Rangers from getting relegated to the Championship at the end of the 2014-15 campaign.
The former Burnley star scored 18 goals and created 23 chances in 35 Premier League appearances.
Austin had a pass accuracy of 66% and a shot accuracy of 67%, and won 86 headers, 15 dribbles and 16 tackles.
The former Swindon Town man has started the 2015-16 season on a positive note, scoring two goals and creating six chances in three Championship appearances.
Austin has a pass accuracy of 65% and a shot accuracy of 50%, and has won eight headers and five tackles.
The QPR forward is an in-demand player in the summer transfer market, with Newcastle United reported to be interested in his services by The Daily Mail, while The Daily Star recently stated that Tottenham want him.