ST KILDA concedes Nick Riewoldt could have been rested earlier in the season, with the champion Saint to miss Saturday afternoon's game against the Western Bulldogs at Etihad Stadium with a knee injury.

Riewoldt, 34, suffered bone bruising to his left knee in the 50-point loss to Sydney last week. It is the same knee that has been problematic for the past few years and often required fluid to be drained.

Riewoldt hyperextended his right knee in round one against Melbourne this season.

The former captain watched on at Friday's training session with his son James as the Saints had a light run at Sandringham, and coach Alan Richardson said the six-time best and fairest could have missed the victory against Greater Western Sydney earlier this month, having carried soreness into the clash.

"He probably wasn't at his best that game. Still did a reasonable job for us structurally, but didn't have a great influence on the game," Richardson said.

"In hindsight, we possibly could have rested him then.

"He was keen to play (and) we were keen for him to play. This one's been taken out of his hands and our hands. He's just a bit too sore."

St Kilda has a bye next week, meaning Riewoldt will have had 20 days to prepare for the Friday night match against Adelaide at Adelaide Oval on June 9.

However, Richardson said Riewoldt wasn't being rested.

"It really just came down to this week," the coach said.

"He bruised his knee on the weekend so we were hopeful that he'd come up, (but) it was pretty clear early in the week that he was still a little bit sore."

Inside midfielder Luke Dunstan was dropped, while Darren Minchington and Shane Savage have been brought in.

Richardson admitted it was tempting to bring Josh Bruce straight back into the side after poor form meant he was left out against the Swans.

"Structurally, it probably makes a little bit of sense, but just his form prior to him going out and then again on the weekend wasn't quite where it needed to be," Richardson said.

"There's a plan in place there. Of course, plans go out the window if you think that person's going to help you win a game of footy, (but) we're happy with the group we've got in front of the ball.

"It'll give us a different look – there's probably a little more speed and energy given that we're going to be a bit smaller."

Bruce kicked one goal in the VFL last week.

Dynamic forward Mav Weller spent time off the ground against the Swans after hurting his right ankle, the same one he rolled at training a couple of days before facing the Giants.

Richardson said there was no concern that would be a lingering issue.

"He's been a little bit sore. He finished the game really positively on the weekend so we'd expect him to roll on from that," he said.

"He's had a good week on the track, he's done every session (and) he's moving well."