He also had to deal with a deep laceration on his right calf last week, which was sustained against Richmond the previous round.
However, the Saints are confident Riewoldt, 32, will be fine to play the remaining six games of the season, with a week's rest expected to be enough to get him through.
"We all know he went into the 'Maddie game' against the Tigers a little bit banged-up in respect to his calf but performed strongly, and was really good last week again but got a knock in his other one," coach Alan Richardson said.
"There is just too much of a build-up in terms of minor injury that we think might lead to something more substantial.
"We want him to be able to finish off the season strongly, so it's just too big a risk, really.
"We just think with a week off [he'll be right to finish the season] - he won't do any training at all, it will just be physio and recovery up until he comes back on Tuesday."
David Armitage also didn't train on Thursday, but Richardson said he was confident the midfielder would get up despite receiving a number of hits, including a nasty kick to the shin, during the win over the Demons.
Gilbert is being troubled again by a groin/thigh issue, which he battled earlier in the season when he was trying to get back from a foot injury through the VFL.
But Richardson said he was confident the problem would not drag on.
"He's a little bit sore in the quad but nowhere near as severe as it was," he said.
"We think we've got it early. The scans just showed a little bit of fluid in the thigh region so we think with a week off he should be right for next week also."
Ruckman Tom Hickey and forward Tim Membrey will come into the selection frame for Sunday's clash with the Power, along with Blake Acres, Josh Saunders and Luke Delaney.
Richardson said American-born ruckman Jason Holmes, who signed a one-year contract extension this week, remained a chance to be promoted this season in place of Jack Billings.
But, after Hickey's strong VFL form last week, it wasn't likely to happen ahead of the Port game.
"His progression has been fantastic. He still has a bit of work to do but he's going really well," he said.
"With a bit of luck, he's even a chance to play League footy this year.
"Both Jason and Ahmed Saad and Brenton Payne are chances to be elevated, so we'll just wait and see but there is a chance that will happen."
Billings won't play again this season and will go on the long-term injury list after scans showed a hot spot in his shin had developed into a stress fracture.
