Parramatta five-eighth Dylan Brown concedes it will be a "massive loss" for the Eels if Mitch Moses is to miss next week's semi-final with concussion.
Moses left the field midway through the second half of the Eels' 27-8 qualifying-final loss to Penrith after his head collided with Viliame Kikau's hip.
Losing their halfback rattled the Eels, who conceded two tries in quick succession to bow out of the contest.
While Moses appeared to have been knocked out by the hit, he was up and about after the game.
He is no guarantee to clear concussion protocols by game day of the semi-final, likely to be Friday, but Brown and the Eels are remaining hopeful.
"It seems like he's fine so hopefully he pulls through," Brown told reporters.
"Obviously if he's not there, it's a massive loss but we've got other people in line."
Jake Arthur came on at halfback after Moses's concussion and looms as the likeliest replacement should the halfback lose his race with the clock.
The son of Eels coach Brad, Arthur filled in at halfback for two matches in August while Moses recovered from a finger injury and had a career-best game against Manly.
"You've seen the way he played when Mitch was out earlier in the season," Brown said.
Brown indicated the Eels would be hoping to sustain the physical start they brought to Friday night's game when they meet either Canberra or Melbourne next week.
"That was how we wanted to play our footy but there were too many errors in the second half and we couldn't get out of our red zone," he said.
"Against Penrith, you need to be down the other side of the field.
"We're pretty shattered with that loss but we're onto next week."