High-level professional football is a fast, intense game full of twisting, straining, collision, impact. The more players are honed into high-endurance power machines slamming into one another, the more vulnerable their ligaments, soft tissue etc. Slender, swervy players like Giggs, who attract fouls, will generally get injured more, but I think this 'prone to injury' thing is a red herring. All pro footballers are 'prone to injury'; some are just unluckier and some never properly recover and play half their careers with underlying injuries that are managed with injections and other treatments. It's always happened; it's their livelihoods after all. They're on game bonuses and the career is short, Nowadays though, the monitoring of these injuries is much more thorough and the medics know the damage that may ensue if someone plays half-crocked.