GREATER Western Sydney expects scans will confirm forward Jonathon Patton needs a third knee reconstruction after the former No.1 draft pick went down in a training incident on Thursday morning.

The unlucky 25-year-old Giant landed awkwardly in a marking drill and is set to undergo scans.

It is understood to involve his left knee; the one he endured patella tendon surgery on in his first year as a Giant.

Patton has had the anterior cruciate ligament on the right side reconstructed twice; once in 2013 after injuring the knee in round three, and again the following season following a round 21 injury that saw him miss the majority of 2015.

"The initial diagnosis for Jon doesn't look positive however we'll await the results of scans on Friday," Giants football manager Wayne Campbell said.

"He has the full support of everyone at the Giants during this challenging time."

Patton has played 89 AFL games since debuting in round 12, 2012, after being selected with the top selection in the previous year's NAB AFL Draft.

He didn't play until the mid-season point of his first season as a Giant after travelling to Sweden for the patella tendon operation in January that year.

After overcoming the run of issues with both knees, Patton put together a career-best season last year to kick 45 goals and take 142 marks in 22 games, and end the year ranked sixth in the competition for total contested marks.

He re-signed with the Giants until the end of 2020 in February last year.