The Hawks will also await an X-ray on skilful defender Jack Scrimshaw's finger.
A breathtaking nine-goal first quarter set Hawthorn on their way, and despite Richmond steadying, Sam Mitchell's charges leapt to seventh with a 19.17 (131) to 10.8 (68) win in front of 58,231 fans at the MCG.
Day was helped off the ground, then sent to hospital, with a right collarbone injury after he and teammate Jai Newcome collided when attacking the ball in the first quarter.
Will Day came from the ground after a bit of friendly fire from Jai Newcombe.— AFL (@AFL) #AFLHawksTigers pic.twitter.com/SZacc0mepBAugust 18, 2024
If Day's injury proves season-ending, it would be a huge blow.
Hawthorn won just one of their first six games while Day, 23, was sidelined with a foot injury, then went 11-4 with him in the 15 games before Sunday.
"He had an X-ray already ... and no break," Mitchell said.
"So, good news, but that's not enough information. So he'll have other tests tomorrow, CTs or MRIs, or whatever the medical team decide.
"He's obviously in a fair bit of pain. We'll support him and and see how nasty it is.
"At this stage, the information I have, he could play next week, or he might not play again for the season. We actually have no idea. You just have to wait another 24 hours."
Claiming a first finals berth in six years is in Hawthorn's hands, given they play 17th-placed North Melbourne in Launceston next Saturday.
Hawthorn (52 points) sit behind fourth-placed Geelong (56), Brisbane (54) and the Western Bulldogs (54) and ahead of Carlton on percentage (52), and Fremantle (50).
"If we win, we play finals. So if I have to help with the motivation, I think we're probably not deserving to be there," Mitchell said.
"The opportunity that's at our door is super-exciting, obviously, but I don't think we're a group that at this point are willing, or have had the lack of mental discipline, to look too far ahead.
"We haven't had that luxury all year, so this week will be another final for us."
Newcombe (33 disposals, nine clearances) and James Worpel (29 disposals, two goals) shone.
Jack Gunston (five goals), Calsher Dear and Nick Watson (three goals apiece) led Hawthorn's attack.
Tigers Shai Bolton (three goals), Noah Balta and Rhyan Mansell (two goals apiece) were lively.
Jack Graham could face scrutiny for catching Cameron Mackenzie high with a late spoil in the second term.
Mansell kicked the opener but Hawthorn responded with nine unanswered goals to lead by 50 at quarter-time.
Richmond cut the deficit to 37 at the long break before the Hawks kicked away again.
"You can't give a team that sort of head start on all phases of the game then expect to reel them in," Tigers coach Adem Yze said.
"So, bitterly disappointed with the way we started and we spoke about that post-match.
"Yeah, there's one thing about responding but there's - two - coming ready to play.
"We didn't as a footy club, and we let our supporters down."
Last-placed Richmond finish their season against Gold Coast at the MCG next Saturday.
