GREATER Western Sydney has received bad news on Dylan Shiel's knee injury, with the midfielder to undergo surgery this week on a torn lateral meniscus.

The silky left-footer will have arthroscopic surgery on his right knee to determine the extent of the injury, which could sideline him for between six to 12 weeks.

If doctors find any significant damage, it will likely put an end to the 22-year-old's breakout season, unless GWS makes it deep into the finals.

Shiel was subbed out of Sunday's 35-point win over St Kilda at Spotless Stadium after kicking a goal before half-time.

The Victorian was pre-selected by the Giants in 2011 as a 17-year-old, and recently re-signed with the club until the end of 2017, ending speculation he would return home at the end of the season.

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Shiel has been a star for GWS, averaging 26 possessions per game in 2015, and should be an early frontrunner in the Brownlow Medal. 

With co-captain Callan Ward, fellow young stars Adam Treloar, Stephen Coniglio and Devon Smith, plus the experienced Ryan Griffen, Shiel has formed a formidable midfield brigade at the Giants this season.

GWS were considered finals certainties when they were 7-3 earlier in the season, but the club got the wobbles after losing ruckman Shane Mumford for the season, and key defenders Phil Davis (ankle) and Joel Patfull (lung/ribs) in a round 11 loss to Collingwood.

There is some positive news for the Giants; Patfull was expected to miss 6-8 weeks but could make an earlier return after missing the past three games.