Greater Western Sydney fear defender Adam Kennedy may have torn his ACL during their shock 23-point loss to St Kilda at Etihad Stadium.
Kennedy landed awkwardly during a marking contest midway through the first quarter of Friday night's game and went straight to the Giants' rooms in obvious distress.
He played no further part in the game as the Saints powered home to a 16.12 (108) to 12.13 (85) victory.
The 24-year-old will undergo scans in coming days but coach Leon Cameron - who has already had to contend with an ACL injury to defender Matt Buntine - says he is fearing the worst.
"We'll find out in a day or two but it's not looking great," Cameron said.
"That's life. He's probably one of our most popular players and he was in really good form. It's disappointing that we've had Buntine and him in the last month but that's what we've got to deal with at the moment."
Kennedy's injury added to a rough night for the Giants, with St Kilda's fanatical pressure proving too much to handle.
Down by a goal at three-quarter time, coach Alan Richardson challenged the Saints to finish strongly after fourth-quarter fadeouts against Geelong, West Coast and Melbourne.
They responded with a dominant final term, booting six majors to one in a performance which showed they belonged on the Friday night stage after a year-long absence.
Jack Steven (29 disposals, two goals) was dominant in the midfield, half-back Dylan Roberton continued his stellar season and young forward Blake Acres sparked the fourth-quarter run with consecutive goals.
"That was the message at three-quarter time - we needed to be strong late and we needed to learn our lessons," Richardson said.
"That was the real positive for me. I wouldn't have said we had 22 contributors at halftime but by the end of the day, the guys had lifted into the game and we had a really even performance."
The Giants were reduced to two players on the interchange bench for most of the second quarter after Nathan Wilson's head was slammed into the turf in an aggressive Koby Stevens tackle.
The tackle was deemed fair at the time - Stevens won a holding-the-ball free kick as a result of it - but the incident is bound to be scrutinised by the match review panel.
Wilson returned in the second half after undergoing concussion tests but the Giants never looked at their best, despite strong efforts from Stephen Coniglio, Tom Scully and Callan Ward.
The Giants led by a goal after Devon Smith's 60m bomb on the three-quarter time siren but the final term belonged to St Kilda, with Steven's outstanding midfield work leading the way.
"It's really disappointing from our point of view because we pride ourselves on our last quarters," Cameron said.
"We just fumbled and lost the hunt. Their clearance work was better and you'd have to say they wanted it a little bit more than we did."