PORT Adelaide co-captain Tom Jonas has been ruled out of Friday night's clash with Collingwood at Marvel Stadium, while vice-captain Hamish Hartlett will miss at least a month after another setback in his return to senior football.

Jonas has a minor calf injury that he sustained at a training session last week that forced him to miss the Power's round six win against North Melbourne at Adelaide Oval.

FULL INJURY LIST Who's ruled out and who's a test?

The 28-year-old is expected to be available for Showdown 46 against crosstown rival Adelaide in round eight.

Meanwhile, Hartlett will be out for the next month with a hamstring injury that is related to the knee reconstruction he underwent last year.

Hartlett has had complications in the area where muscle was taken to help repair the torn ACL in his knee last year.

MID-SEASON DRAFT 50 players who could spark up your list

"Unfortunately, Hamish is having some issues with the graft site from the ACL operation he had last season," the Power's head of medical services Tim O'Leary said.

"He is working through the appropriate progressions to return to full fitness over the next month or so."

Hartlett has missed the past four SANFL games with hamstring soreness.

The half-back flanker played the last of his 153 AFL games for the Power in round five, 2018.

Find Trends on Apple Podcasts, Google Podcasts and Spotify