Speaking after the Saints' 28-point win over Collingwood, Lyon said he believed Riewoldt's injury was less severe than that suffered by Essendon spearhead Matthew Lloyd in 2006, which forced the former Bomber to miss the remainder of that season.
The injury occurred during the last minute of the second quarter, when the St Kilda captain jumped to mark with his Collingwood opponent Simon Prestigiacomo right behind him.
Riewoldt immediately grabbed at his right hamstring mid-leap and fell to the ground, grimacing in pain.
He headed straight to the rooms for treatment and spent the rest of the match on the bench.
"If I thought it was off the bone, you reckon I’d have half a smile on my face now?" Lyon said.
"He’s a special player. All of the St Kilda people don’t want to see him get hurt.
"We don’t think it is that significant - we will let you know."
With Riewoldt set to undergo scans in the coming days to learn the full extent of his injury, Lyon has already started planning to fill the void created by his skipper's inevitable absence.
"It’s going to be a challenge - no doubt about that. He is a key forward, he is pretty special... but we proved tonight we can cope," the Saints coach said.
"Koschitzke will be back soon... and Gardiner is pretty good forward, so we will have to improvise."
"Everyone else has challenges and obviously it is a significant one but one we are looking forward to coping with. "
The injury overshadowed a fantastic team effort by the Saints, who kept the Pies goalless in the second half despite losing Sam Fisher (mild concussion) and Lenny Hayes (broken nose).
Remarkably, Fisher returned to the field in the final quarter and both players are expected to be available for selection in the twilight game against Fremantle next Sunday.
"I thought it was a magnificent effort - everything was thrown at us, and we responded like good teams do," Lyon said of his team's resilience.
"As a home and away game - the merit of the four points under extreme adversity… was really valuable for the belief."
Lyon paid special tribute to Stephen Milne, who worked hard in the absence of tall forwards Riewoldt and Koschitzke in the second half.
