RICHMOND defender Nick Vlastuin remains "doubtful" for Sunday's clash with Hawthorn after being substituted out of the round-one win over Carlton with a knee injury.

But the Tigers are certain to be bolstered by the return of captain Trent Cotchin against the Hawks after the experienced midfielder missed the season-opener with a bout of gastro.

Vlastuin hyper-extended his knee with a fresh-air kick and was replaced by teammate Jack Ross during the third quarter against the Blues.

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The next day, Vlastuin denied the Tigers had gamed the new medical substitute system and scans later revealed he had squashed the fat pad in his knee, which caused bleeding.

The Tigers rate Nick Vlastuin's hardness at the content. Picture: AFL Photos

The triple-premiership defender was due to train at Punt Road on Friday, with the team to take on Hawthorn set to be named on Saturday.

"He's probably still doubtful at this stage, but we'll see how he goes at training," Tigers coach Damien Hardwick said.

"He's such an important player for us that we won't push the envelope on him this early in the season.

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"We'll just see how he goes, but he's probably doubtful at this stage."

Hardwick isn't concerned about the possible bad look of Vlastuin playing the week after being substituted out of a match through injury amid ongoing concerns clubs could rort the medical substitute system.

"From our point of view, it's a bigger deal outside the AFL industry than in," Hardwick said.

"The fact of the matter is Nick's probably in our top-five best players, so we're not necessarily going to sub a really good player off to put on our 23rd player."

Cotchin was a late withdrawal from the Carlton game and lost a significant amount of weight over a 48-hour period when he didn't eat or drink a lot.

But he trained the following day and has no lingering concerns this week.

Trent Cotchin in action. Picture: AFL Photos

"He had the gastro complaint towards the back end of last week and, especially with the way the game is played early doors, it was always going to be tough for him to play," Hardwick said.

"We made the call just to park him and we'll look to welcome him back this week.

"He's so important to the way we play and the way he leads his team is incredible.

"The way he plays the game is inspirational to our players, so it's great to have him back."