MELBOURNE premiership defender Trent Rivers is racing the clock to be available for round one after the club revealed he suffered a knee injury during the practice match against North Melbourne last week at Casey Fields.

Rivers played the game out, but follow-up imaging showed he has a low-grade PCL strain that will sideline him for 3-4 weeks.

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Melbourne's opening round against the Western Bulldogs is exactly three weeks after the injury occurred.

Rivers is one of a handful of Demons defenders carrying niggles, although the club says the rest are on the minor side.

Therabody AFL All-Australian full-back Steven May and veteran defender Michael Hibberd have "a little bit of tightness" – as described by the club's performance manager Selwyn Griffith – and will miss Thursday's AAMI Community Series match against Carlton.

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But the club is adamant both will play in round one.

Christian Salem (knee) will also miss against the Blues but is expected to be fine for the season-opener. Salem had an incident at the end of the practice match where a North Melbourne player fell across his knee.

Harrison Petty is a little further away though following surgical intervention on a corked calf.

"He is progressing well and has integrated into running," Griffith said.

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"He’ll look to return to performance in the next 3-4 weeks."