The Hawks today confirmed the 25 year old had suffered the horror injury at this morning's session at Waverley Park and will now need surgery.

An ambulance was called to the training ground to take Mitchell to hospital after the star went down as they practised clearance work.

The midfielder's rehab is set to stretch well into the upcoming season and he's unlikely to be back fit in time to play any part in this year's campaign in a massive blow to the Hawks' flag hopes.

Hawthorn general manager of football Graham Wright added: "For Tom to suffer an injury like this is incredibly disappointing for both him and our footy club.

"He will undergo surgery over the weekend and as a result will most likely miss the 2019 season.

"However Tom is a very resilient young man and we have no doubt that he will tackle his rehab with the same professionalism and diligence with which he approaches his training."