The Hawks’ superstar suffered the injury during a drill as the club returned to training at Waverley Park for their first session of the new year.
Mitchell will undergo surgery and isn’t expected to return this season, indicating the severity of the injury.
“For Tom to suffer an injury like this is incredibly disappointing for both him and our footy club,” Hawks football boss Graham Wright said in a statement.
“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.”
An ambulance was driven onto the club’s Waverley Park oval and a Hawthorn doctor accompanied Mitchell as he was taken to hospital.
Mitchell, the runaway winner of his first Brownlow last September, is one of the league’s top midfielders.
The Hawks lost their two finals in 2018 to finish fourth, but, after missing the finals the year before, they had been bullish about their prospects this season.
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