MATTHEW Kreuzer is no certainty to play next week, after Carlton coach Brendon Bolton revealed the Blues ruckman had concussive symptoms following last weekend's loss to Collingwood.

Kreuzer rolled his left ankle during the second quarter against the Pies, was forced from the ground just after half-time and didn't take any further part in the game.

But what was first reported as solely an ankle injury has since become more serious.

"(Kreuzer) has got an injured ankle and he's got some concussive symptoms as well," Bolton revealed on Friday morning.

"The combination of those two [injuries means] we don't want to take a risk.

"Because he's such a competitive and combative player, we really have to save him from himself."

It's unclear when the incident that caused Kreuzer's concussion was, but the Blues coach said the ruckman was still showing signs of a concussion post-game.

"My understanding is that there were still concussive symptoms late after the game," Bolton said.

"I found out (about the ankle injury) in-and-around half-time, but I was briefed that (the concussion) in combination with his ankle is what stopped him later in the evening after the game."

Bolton is hopeful Kreuzer will only miss Saturday's fixture against Port Adelaide at the MCG, and ensured the 200cm big man's health is the main concern.

"We're optimistic Kreuzer will be back next week, but I can't be totally definitive on that," Bolton said.

"We'll make sure 'Kreuze's' welfare is the number one priority."