There is a huge difference between a torn cruciate ligament and a shattered ankle joint held together with screws and plates. His hamstrings are like cheese strings too.
Katz didn't always give 100%. He often had times where he couldn't be bothered. I can remember him in an under 21s match where Gus came to watch him, to give him one more chance.
Kaz fell out with Ian Holloway & was sent back early from his loan, some of which was turning up late for training...