The 20-year-old is expected to be on crutches for about six weeks and the club says his status will be reviewed in three months to determine whether he can begin running.
“At this stage we can’t tell when Jarryd will be able to return, but he will be sidelined for at least six months," football manager Greg Hutchison said on Saturday
"It’s a disappointing blow for Jarryd and the club, which comes at a time when the list is almost completely healthy and looking forward to a strong pre-season.”
Allen was drafted 59th overall in the 2006 NAB AFL Draft and has played four senior games for St Kilda since making his senior debut against Fremantle in round 13 this year.
