Day kicked the ball through the middle during Sunday's match at the MCG and was crashed into late by Ryder.
The 20-year-old was helped from the field and substituted out of the match at half-time.
Ryder was on Monday charged with rough conduct, with his actions assessed by the match review officer as careless conduct, high impact and high contact.
St Kilda coach Brett Ratten said post-match the bump looked "pretty fair" after watching replays of the incident.
But captain Jack Steele said the incident was a reminder to all players that opting to bump an opponent can lead to trouble.
"At the end of the day, I suppose, it's a player's choice whether they bump or not," Steele said.
"You just can't get them high, can't get them in the head.
"Paddy went for the bump and it was a bit unlucky."
St Kilda will decide on Tuesday whether they challenge the ruling.
If suspended, Ryder will miss games against Gold Coast and GWS, with mature-age recruit Jack Hayes in line to return as his replacement.
"What we love from Paddy is obviously his tap work but his follow-up as a ruckman as well is so crucial," Steele said.
"Being a physical player in the contest is something that he's really good at and he makes us all walk taller when he does it."
Day will miss Hawthorn's Easter Monday clash with Geelong under concussion protocols.
Hawks players remonstrated with Ryder after the collision, which coach Sam Mitchell said left Day "a bit battered ... a bit sore and sorry for himself".
Melbourne forward Ben Brown will spend more time out of AFL action after he was hit with a suspension for striking Williamstown's Max Philpot in the VFL.
Brown missed round three through COVID-19 protocols and returned via the Demons' state league affiliate Casey.
He kicked two goals but was found guilty of striking Philpot in an incident assessed as intentional conduct with low impact and high contact.
The two-match suspension can be reduced to one match with an early guilty plea.
Sam Weideman is likely to retain his AFL spot in Brown's absence.
Adelaide young gun Josh Rachele was hit with a $2000 fine for striking Essendon's Devon Smith in the same match that he earned a Rising Star nomination.
Gold Coast's Ben Ainsworth and Carlton's Nic Newman copped $1000 fines for wrestling each other, while Blues forward Harry McKay received a $1000 fine for staging.
Essendon midfielder Darcy Parish was fined $2000 for tripping Adelaide's Braydon Cook.
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