Collingwood captain Nick Maxwell will miss the start of the Magpies' AFL premiership defence.

Maxwell, who has not trained since copping a heavy knock which caused bleeding to the kidneys more than a fortnight ago, said the best-case scenario was a round two return, although it could be as late as round four.

That is despite the skipper receiving a positive assessment from a specialist about his internal injuries, after being scanned on Monday.

He was told that while he cannot play against Port Adelaide at Etihad Stadium on Saturday, his body will have healed well enough to cope with match-play a week later against North Melbourne.

The catch is, having been warned against doing any exercise whatsoever since the injury, he is unsure whether he will be fit enough to play by then.

"I took that seriously, I've done nothing for two weeks and now basically I've just got to try to get the conditioning back," Maxwell said.

"You de-train a fair bit in two weeks, so I've just got to make sure I'm right for whenever it is I'm back.

"The Collingwood doctors and physio staff will make a decision over the next two, three, four weeks, whatever it is."

Maxwell said, under medical instruction, he had not even walked or lifted anything for a fortnight.

"If I stuffed that up, that two weeks, did too much and lifted and caused the injuries to re-tear or not heal properly it could have been a lot more (time off) and been serious."

He has been cleared to start exercising on Tuesday, but to stop if it causes too much pain.

Maxwell cannot resume contact training until at least next week, with the intensity also pain-dependent.

But he has been assured that once he does return to the playing field there is no increased likelihood of a repeat injury.

"Any time you heal with anything, you tend to heal stronger," Maxwell said.

"For me that was the main thing, to get the internal stuff ticked off.

"Then the rest of it, obviously pain is something you're aware of and you know the limitations, so get the conditioning right and go from there."

Maxwell's absence for at least the first round means Collingwood will be missing at least two first-choice tall defenders, as fullback Nathan Brown (knee) is out for the season.

The club is hopeful another key backman, Ben Reid, will play against the Power, although he faces a test of his recovery from an ankle injury.

Small forward Brad Dick, who is on the comeback trail from shoulder injuries which ruined his 2010, is the only other first-choice Magpie in doubt.

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