Return to sport after patella fracture

Hello

I'm hoping for some advice on rough timeframes for returning to rugby after a patella fracture. It's for my 11 year old son so I want to make sure that he is fully rehabilitated before playing again.

He chipped his patella during a hard tackle and was in a full leg cast for 4 weeks, he has been doing some static exercises but we haven't really been given any guidance as to how long it will be before he can play again. He's keen to get back to it but we don't want to exacerbate it as there is obviously no way of having a gentle re-introduction to contact rugby.

He has been walking on it and has had no pain whilst doing gentle knee exercises but any ball park figures of how long he should wait before re-joining his team-mates would be much appreciated.

Thanks

Stu