SYDNEY will be without key tall Sam Reid for the rest of the season after he underwent hamstring surgery on Tuesday.

Reid injured himself in Sydney's final pre-season game in March and while the club initially hoped he would be sidelined for a matter of weeks, he was placed on the long-term injury list a month ago.

With the 31-year-old not showing enough progress through his rehabilitation program, the club decided to operate this week, ending his season.

Reid comes out of contract at the end of this year.

One of the most important members of the Sydney side when fully fit, Reid has had a horror run with injury since joining the club in 2010. He missed the entire 2016 season and all but one game in 2018 and has played 181 matches of the 320 Sydney has played since he was drafted, which is a little more than half.

"We had hoped Sam could return from his injury and avoid surgery, but unfortunately it became apparent last week that wasn't the case," Swans GM of footy Charlie Gardiner said.

"The initial injury was not straightforward and we wanted to ensure we explored all possible options for Sam to return as quickly as possible.

"Sam has done everything in his power and worked exceptionally hard to get back to play, so it's incredibly disappointing for him and the club that he will miss the season.

"The initial feedback is that the surgery went well. He will start recovery immediately and will continue to help develop our emerging tall forwards through the remainder of the season."

Reid's most recent AFL game was last year's Grand Final, where he was picked despite injuring his adductor in the thrilling preliminary final win over Collingwood.

He was substituted out of Sydney's 81-point loss in the third quarter after hobbling from the ground just before half-time and coach John Longmire later admitted playing him was a mistake.