A SEVENTH concussion since 2014 will sideline luckless St Kilda forward Paddy McCartin for Saturday's clash against Fremantle, after he was originally diagnosed with whiplash.

There is no guarantee he will return on Saturday week against Collingwood.

McCartin, 22, passed the concussion test after a nasty head clash with Melbourne defender Neville Jetta in the second term but a later incident with James Harmes saw him suffer whiplash.

Coach Alan Richardson said after that game McCartin was "all clear" from a concussion perspective.

McCartin has recovered from the neck soreness from that incident but has experienced nausea and fogginess.

While he trained in the gym on Thursday and did some work with the football, the No.1 selection from the 2014 NAB AFL Draft was kept away from the main group.

"The (original) diagnosis was a mild form of whiplash and since then, he hasn't quite been right," coach Alan Richardson told reporters at Melbourne airport on Friday.

"The docs will do whatever they need to make sure that he's right to go.

"He's done a little bit of light training. He did a little bit yesterday and was feeling OK. My understanding is he's still got a little bit of work to do with the medicos to give the all-clear to get back out.

"We're hoping it might just be this week that he misses. It might be a couple. We'll just wait and see how he responds."

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McCartin suffered his last concussion in June 2017 and did not return for the rest of the season.

His run of seven straight games to start the season was the longest of his 29-match career.

"Often when you get whiplash it can cause concussion-like issues. There's no doubt he's pulled up a little bit groggy," Richardson said.

The Saints have won just once this season and head to Optus Stadium as they try to break out of their rut.

Leadership group member Jack Newnes and gun forward Jack Billings have been down on form, which Richardson acknowledged.

"They would be the first to admit that they haven't been as strong as they have been for us," Richardson said.

"Both players have been really good for a couple of years now. They've been down a bit. We definitely need them to respond."

Newnes has laid only four tackles through seven games this season, although he was concussed late in the first quarter against Greater Western Sydney.

"That's a real strength of Newnesy's. He certainly hasn't been where we want him to be in that space and I expect him to respond," Richardson said.

Debutant Ed Phillips will mostly line up on a wing while Blake Acres, who missed last week with a groin issue, will split his time between the midfield and forward line.

St Kilda will focus on speeding its transition when going from defence to offence.

"There's a little bit of hesitation in our play. There's a little bit of uncertainty. Guys, probably too many, second-guessing themselves on the back of probably being too concerned about being scored against," Richardson said.

"That can happen when it is you're down a little bit on form. We need guys to be bold with their footy."