It could be anything, its impossible to say without seeing the training, preparation, recovery and conditioning methods employed by each. There was a LOT of 'soft tissue' injuries under Mary's reign that disappeared with Hickmans, who was clearly more qualified in the field of sports science. But there are countless factors that lead to injuries that COULD have been directly attributed to McGregor's methods. Again, impossible to say without knowing said methods.
Best recent case is that of James Tedesco. Kid always had talent, but for the past few years has struggled to string games together withour copping a leg injury. Not just in top grade btw. Taylor came in and his team identified an issue with Teddys running style, trained him to amend it, and hes got a full season out so far. Good S&C can work wonders.