After struggling to keep up with his teammates over pre-season, Gold Coast key forward Sam Day has been relieved to find out why – a 10cm bacterial cyst in his stomach.

In late December it became clear the 196cm big man was battling illness.

Soon after, the reason for his lack of energy and loss of weight was discovered.

"This has been a long running one, ever since he started back he hasn't been himself,'’ SUNS football manager Marcus Ashcroft told the Courier Mail.

"We didn't know what was wrong, we weren't sure if we needed to push him harder.

"Eventually in late December it became obvious there was a medical issue.”

"In a way we are glad there was an issue, because it explained everything for us, and for him.

"It was a bit of a relief for him.

"You can imagine as a player and you want to get better, and he is certainly a driven person who takes pride in his performance, he was seeing everyone else getting better and he was falling behind and he started to doubt himself.’'

Day could have had the cyst burnt out, but with the Christmas break coming up it was decided medication and rest would aid his recovery.

It is unclear where Day picked up the cyst, although the SUNS believe it could have been when the former No.3 NAB AFL draft pick holidayed in Fiji.

Now the issue has been resolved, they are confident Day will be fit to add to his 64 career games by round one.

"(Returning to training on Monday) would have given him a lot of confidence because he was able to get out there and train and he was moving well,'' Ashcroft said.

"We've still got two months to get him fit so we aren't worried about it all.’'