"There is a possibility you may not have done as good a deal as you would have hoped but that's the landscape if your client wants to move forward now," Gillis told AAP.
"If I was a player I would be making a bit of noise about it.
"I wouldn't call it guess work but there is a need to put a fair amount of judgement into how it all unravels."
The NRL is yet to finalise a 2018 cap figure amid ongoing collective bargaining agreement talks.
Gillis hopes the NRL provides a cap deadline sooner rather than later - but fears the worst.
"I have heard it might be April, May or as late as October next year," he said.
"By those dates most, if not at all, prominent players have done their deals by then - it does make it very difficult."
It is believed the likes of Thurston hope to sidestep the drama by negotiating a percentage deal in which his wage is adjusted once the cap is finalised.
But leading agent Gillis warned: "The vast majority of clubs have ruled out putting in triggers in for players because they have been caught in the past and miscalculated where the deal may end up.
"They can't always be the most reliable option.
"It comes back to forecasting, making judgements, having a reasonable idea of what is more likely to happen."
For the record, Gillis hoped the 2018 cap was more than the reported $10 million mark.
He was just unsure how the figure could be reached.
"I am a believer in the players getting their fair share of the pie," Gillis said.
"If you ask me I think it should be more than $10 million.
"(But) we have spoken about extending squads from 25 to 30, bringing in rookies, increasing the minimum wage, putting more money into retirement funds, all that sort of thing.
"It's all a bit of an omelette at the moment."
- AAP
