Gilmore, who played the first seven games of the season, has experienced constant dizzy spells and lethargy since the knock.
The 25-year-old has not played a match since June 14 when he lined up for South Fremantle in the WAFL and Fremantle coach Mark Harvey conceded he did not know when Gilmore would be able to play again.
"He copped a heavy knock at training a couple of weeks ago and he's been having ongoing symptoms at the moment so we are monitoring it at this stage," Harvey told Fairfax radio.
"He hasn't been able to train for the last two weeks so he's in constant conversations with our doctors at the moment and just working through that situation."
Meanwhile, Harvey said he was happy with the chemistry ruckmen Aaron Sandilands and Robert Warnock were building but was still not satisfied with his team's clearance work.
Sandilands and Warnock combined for a mammoth 55 hit-outs in Fremantle's four-point loss to Essendon on Sunday.
Although the Bombers managed only 12 of their own, they still won the clearances 41-34 as Mark McVeigh and Jobe Watson lurked at ground level to shark Sandilands' taps.
"It wasn't a huge margin in the result [of the clearances] but obviously when you have 60 hit-outs you are looking for a better return on what we are getting," Harvey said.
"I think what we are doing is we are mixing it up [where we hit it] a lot better [but] what we've got to do is capitalise on it."
Harvey praised Sandilands and Warnock for adding other dimensions to their game.
"They are really starting to gather momentum as a duo, really starting to put in beyond the rucking," he said.
"What I liked was when we lost those three players (to injury against the Bombers) they actually had to fill the void a little bit with the running capacity and I thought throughout the course of the game both of them did that, and gave us different options when we needed to move the ball quickly, particularly down forward."
