A new knee injury has ruined Charlie Curnow’s AFL pre-season.

The Carlton young gun was undergoing more surgery on Thursday after an accident left him with a fractured right patella bone.

That will sideline him for three to four months.

The 22-year-old key forward, one of Carlton’s best young talents, originally needed surgery on his right knee early last month after he was hurt playing social basketball.

Curnow had not played since round 15 because of his right knee and coach David Teague said they had wanted him to do activities such as basketball to test how the joint was recovering.

But this week’s new injury is disastrous.

“The recovery time for a fractured knee cap is typically three to four months,” said Blues football boss Brad Lloyd.

“This will delay his return to running until the new year, which means it is unlikely he will be available for our pre-season games.”

Carlton said in a statement that Curnow had slipped on tiles while walking upstairs and added it is a new injury.

“When Curnow slipped, he produced a high-level contraction to his quadriceps muscle,” the Blues said.

“This caused a large force to go through his whole knee and his de-conditioned patella did not tolerate the load.

The Blues remain confident that Curnow will still play next season.

“Charlie is understandably very disappointed … he is a resilient character, and we have no doubt, knowing the competitor he is, he will be back to playing good football in the navy blue in 2020,” the club said.