Fremantle AFL forward Cam McCarthy is recovering in hospital after his sudden collapse at training and will undergo tests to determine what caused the incident.
The 25-year-old was standing at the back of a line during a non-contact training drill when he fell during a session on Wednesday morning.
Coach Justin Longmuir said McCarthy was able to walk to a waiting ambulance while accompanied by a doctor before being taken to hospital.
"Our medical staff were on the scene really quickly and dealt with it really professionally," Longmuir told reporters.
"I spoke to him this morning and he seemed in good spirits.
"There can be a lot of things that can lead to this. He's in hospital now and he'll get checked over and we'll hear more shortly.
"It's obviously not a good thing seeing someone collapse and players being around that as well."
The club was not aware of any similar issues in the past, Longmuir added.
Fremantle are set to depart on Tuesday for the Gold Coast, where they will spend at least four weeks in a hub to restart the season.
The Dockers intend to take every player on their list, including those in rehabilitation, given their doctors and physios will also be flying to Queensland.
Both WA clubs have also been given AFL permission to take 30 staff as opposed to the 25-person cap imposed on others.
Longmuir said key forward Jesse Hogan was a chance to face Brisbane in round two but the club would not rush his return.
The former Melbourne spearhead went on leave in January to focus on his mental health and hasn't played since June last year.
"He's only done 20 minutes of match sim in the last year so we've got to make sure he can back up sessions, make sure we're confident he can run out a full game," Longmuir said.
"We don't want him in for one game, getting sore or injured or not being able to handle it.
"But every indication is that he's on the right track, both mentally and physically."
Fellow tall Matt Taberner is expected to be available for round two after missing training earlier this week with back soreness.
Longmuir said defender Nathan Wilson (toe) was also tracking well and approaching a return to the main training group.
The Dockers are unsure when they'll get the chance to train on the Gabba ahead of facing the Lions on June 13 but have adapted the dimensions of their training ground accordingly.