The loss left the Storm facing an elimination game next Saturday against the winner of today's Canterbury-Newcastle clash.
The Storm will wait until after the MRI scans to make a call on Waqa's availability for the game.
"The (CT) scans came up clear which was great," Storm football manager Frank Ponissi said.
"Our medical team believe he'll be cleared of any serious injury ... we're very optimistic."
Farrell was placed on report for putting Waqa in a dangerous position, though the rules state that defending players are permitted to tackle attacking players in the air.
While the dangers are obvious, Storm coach Craig Bellamy admitted the incident exposed a grey area in the game's rules.
"It's six of one, half dozen of the other - do you just let him stand there and catch the ball over the line and you can't tackle him till his feet hit the ground?" Bellamy asked.
"Well there's going to be more kicks and there's going to be more tries from kicks.
"Certainly Dylan meant no ill health to Sisa but he tackled him early, before he had the ball.
"He knocked him off balance before he even had the ball - that was the reason it ended up so ugly," said Bellamy.
"I suppose that's just an incident that's been waiting to happen with that rule, but it's a hard one if you go the other way."
- AAP
