The striker missed the defeat to Stevenage at the weekend due to an ankle injury sustained against Tranmere.
Hawley was absent from training at the beginning of the week, but Knill is hopeful he will be available for selection against the Bees.
"He will go for a scan at some point this week," Knill told The Iron Player.
"It's just a precaution really, just to make sure. Karl didn't train on Monday and he's going to have a scan on it, but I spoke to the physio and he doesn't think it's too bad.
"Somebody fell on top of him (in the Tranmere game) but at the time, during the game, he said it wasn't a problem, that's why he kept on playing. There was some swelling afterwards, which we hope will have gone down by Saturday."