ZAC WILLIAMS and Eddie Betts have been ruled out of Carlton's crunch clash with St Kilda, while Coleman Medal leader Harry McKay is only an "outside chance" to return this week.

The news is a hit to the Blues' football department, which is under the blowtorch of a wide-ranging external review that began this month.

It comes with Carlton's finals hopes hanging by a thread as they sit six points out of the top eight with four rounds left to play.

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Williams (hamstring) and Betts (ankle) were injured during last Saturday's horror defeat to last-placed North Melbourne, which McKay missed because of a toe injury.

"Zac Williams injured his hamstring on the weekend, just before half-time," Carlton high performance boss Andrew Russell said.

"It's a pretty low-grade hamstring and we expect him to miss two or three games, so we're a good chance to see him right at the back-end of the season again.

"Eddie's ankle, he was sore initially but actually settled down pretty well.

"He was a bit restricted during the game but has pulled up pretty sore and swollen.

"We certainly won't see Eddie for the next week or two."

Eddie Betts soars for an attempted mark before hurting his ankle against North Melbourne in round 19, 2021. Picture: AFL Photos

Betts' injury could potentially signal the end of his wonderful career, with the 347-game veteran out of contract at the end of the season.

He has kicked 637 goals in stints with Carlton and Adelaide but will turn 35 in November and is no certainty to be offered a new deal.

The Blues have been bullish on Charlie Curnow's progress in recent weeks but it remains to be seen if the key forward will make his long-awaited return from a series of knee injuries against St Kilda.

Curnow has not played a senior match in more than two years but has impressed in two scrimmages this month.

"He had an increase in game minutes (last week) and we were pleased with the way he moved and more pleased with the way he has pulled up," Russell said.

"His knee is great. He's progressing really, really well."

Charlie Curnow at Carlton training on June 21, 2021. Picture: Getty Images

Mitch McGovern has played just three matches this season, most recently in round seven, and will play at the lower level this week after overcoming a hamstring injury.

"'Gov' has had a really good block in the last month," Russell said.

"We're really pleased that we're going to see him playing some footy this week."

Former captain Marc Murphy has "pulled up well" after returning from a calf injury as the medi-sub against North Melbourne.

The veteran midfielder, who needs three more appearances to reach the 300-game milestone, is in the selection mix to face St Kilda this week.