Patrick Dangerfield is in serious doubt for round one of the AFL season after suffering a hamstring injury during Geelong's four-point trial match loss to Essendon in Colac.
The 2016 Brownlow Medallist limped to the Geelong rooms after pulling up sore late in the first quarter.
Dangerfield played no further part in the game as the Bombers ran out 15.11 (101) to 15.7 (97) winners in front of a 9,115 crowd at Central Reserve.
The injury leaves the Cats facing the prospect of being without Dangerfield and fellow superstar Gary Ablett for their opening-round clash with Melbourne on March 25.
"We don't know too much at this stage. We obviously know that there's tightness in the hamstring," Cats assistant coach Corey Enright said.
"Probably the next couple of days ... we'll get some more information around that and see how he is.
"It's obviously really early to tell too much and how significant it is. We need to get the scans and talk to the medicos and see where it lands in the next couple of days."
Dangerfield has only missed one of 49 possible matches during his two years with the Cats.
Ablett trained on Sunday but is also no certainty for round one.
The 33-year-old was sidelined for both of the Cats' trial matches after suffering a hamstring strain last month.
"It's really hard to say at this stage," Enright said.
"All I know is that he's the ultimate professional and he's going to give himself the best chance. There's obviously a fair bit of time to come between now and them so hopefully ... I'd like him out there."
Geelong ruckman Rhys Stanley will also have scans after leaving the ground early on Sunday with a calf strain.
Essendon had their own injury scare with defender Martin Gleeson carried off in the fourth quarter after rolling his ankle.
"You never know how bad (they are)," Bombers coach John Worsfold said.
"You've got to wait a few days obviously but he's got a couple of weeks (to recover)."
The Bombers trailed by 27 points at three-quarter time but kicked four straight goals to open the final term and snatched a match-winning lead through Jake Long in the dying minutes.
Star recruit Jake Stringer impressed for the Bombers with two audacious goals and young guns Zach Merrett and Andrew McGrath were typically industrious.
Forwards Tom Hawkins (five goals) and Daniel Menzel (four) starred for Geelong.