Australian Rules player Dylan Roberton has spent the night in hospital after his frightening collapse during St Kilda's AFL loss to Geelong.
Saints defender Roberton had lined up for a centre bounce in the second quarter on Sunday at Kardinia Park when he suddenly fell to the ground.
Concerned teammates and Saints medical staff quickly went to the 26-year-old and he was able to walk off the ground.
St Kilda football manager Simon Lethlean said further tests were being carried out at Geelong's Epworth Hospital after the initial diagnosis of an irregular heartbeat.
Roberton does not have a history of heart issues, Lethlean said, with an update from club medicos due on Monday morning.
"I think the doctors described it as arrhythmia ... but that's just the on-the- spot diagnosis from what Dylan said himself - quite faint and dizzy and just blacked out," Lethlean told Melbourne radio RSN.
"He then had some tests and there was irregularity with his pulse.
"But obviously, the vision was quite distressing and (it's) a serious incident to make sure he's covered off properly so he's having a number of tests and we'll get an update this morning.
"We're taking it quite seriously, as you'd imagine.
Lethlean said Roberton's teammates were distressed about the uncertainty around his wellbeing.
"With breakages and knees, you probably know what's ahead," Lethlean said.
"I think for this one, it's probably a different feeling for players who saw it, or didn't. To see a guy collapse is a far different scenario than a collision or something.
"So I think it probably quite rightly shook a few of the players up and they were really keen to understand Dylan's whereabouts and health."