I don't know how I missed this the other day but I've finally found out what Matias' injury actually is. Whilst reading translated articles the word 'Pubalgia' kept coming up, I presumed it was some slang that was not recognised. Then this morning I had the idea that I'd heard of 'Pubalgia' before. So one Google search later and we have the answer. Matias is suffering from an Athletic Pubalgia otherwise known as a sports hernia. It's clear now why he's being eased back they don't want to risk straining it more because it may end up requiring surgery.