CARLTON coach Brendon Bolton admits he can't be certain if Matthew Kreuzer's heart trouble will be career-threatening, conceding the star ruckman needs to undergo more testing before being given the all clear.

Kreuzer was named to return on Sunday after suffering an elevated heart rate in round 17 but was withdrawn before the Blues' 29-point loss to Fremantle.

The 29-year-old flew to Perth but experienced concerning symptoms during a light run on Saturday and will be sidelined for the rest of 2018.

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Bolton was worried for the big man and hoped Kreuzer's heart problems wouldn't be a long-term issue that jeopardises his playing future beyond this season.

"I'd like to think not. I think these things can come under control – as we thought it did – but you've got to go and do the testing to find that out," Bolton said.

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The Blues will send Kreuzer back to a cardiologist and know more about his condition in the coming weeks.

"His heart rate is getting elevated – or it has twice now – when he's exerting himself," Bolton said.

"It came down pretty quickly (on Saturday). It was only for a small amount of time, but that's enough to say you don't take any risk.

"We thought it was all on track, ready to rock and roll."