Western Bulldogs utility Lin Jong is set for a long stint on the sidelines after suffering a serious hamstring injury at training.
Former captain Easton Wood also suffered a hamstring injury earlier this week, but his is only a minor setback.
Jong took a break from football last year to manage his mental health, following a torrid run of injuries that included two broken collarbones, a fractured jaw and a serious knee injury.
The full extent of the 26-year-old's latest injury is unknown.
"Lin has suffered a high grade hamstring injury," Bulldogs medical services manager Chris Bell said.
"It was during our match simulation session (on Wednesday) and he pulled up after accelerating.
"We're going to work through a process with Lin over the coming days to determine the extent of his injury and his return to play plan."
Wood, who handed over the captaincy to Marcus Bontempelli this year, will be sidelined for a fortnight after tweaking his hamstring on Monday.
The defender is expected to return in the Bulldogs' second pre-season series match, against Port Adelaide on March 7.
"Easton suffered some low-grade hamstring tightness," Bell said.
"Being this time of year, we don't want to take any risks with Easton, so we're going to back off his training for a couple of weeks."
The Bulldogs have been buoyed by Tom Liberatore's progress, with the tenacious midfielder ramping up his pre-season program after his 2019 campaign was cut short by a knee injury.
"(Tom) is building up his match fitness and at this stage will put his hand up for selection in the first few weeks of the season," Bell said.
In more positive news for the Bulldogs, Taylor Duryea and Riley Garcia are back running as they continue their rehabilitation from significant injuries.