The lingering effects of Michael Robertson's concussion are concerning Manly coach Des Hasler and frustrating the side's top try scorer.

Robertson has missed Manly's past two games and Hasler on Tuesday ruled him out of Sunday's Brookvale Oval clash with the Roosters.

He said the problem flared up after a game against Newcastle in mid-July.

"He's still getting over a bout of concussion, so the doctor is a little bit concerned about it," Hasler told reporters on Tuesday.

Hasler revealed Robertson was getting some scans done and visiting a specialist on Tuesday and the club would have a better idea of his condition later in the week.

"He's having a few headaches, he's seeing the necessary doctors and specialists, something like that you treat seriously," Hasler said.

He doubted Robertson was suffering the 'footballer's migraine' condition that had sidelined Wallabies star Berrick Barnes for parts of the rugby season.

"Probably not, the pain could be radiating from somewhere else, but that's what they will check out," Hasler said.

It has been a difficult couple of months for 28-year-old Robertson, who had a run of 139 straight games snapped in May by a knee injury.

The Scottish World Cup representative missed three games with that issue and played three more, tallying his 200th first grade appearance, before the latest problem arose.

Robertson remains Manly's top try scorer and joint fifth highest in the competition with 11, despite being sidelined.

Asked if the concussion issue was getting Robertson down, Hasler said: "He's a bit frustrated with it."

Hasler said if Robertson received the all clear from the specialists, he could resume training later in the week, even though he wouldn't play against the Roosters.

Manly could however get back another winger, with Hasler saying Tony Williams had a pretty good chance of returning this week from a hamstring tear, which has sidelined him for five games.

Second-placed Manly are four points behind ladder-leaders Melbourne following last week's loss to Wests Tigers and Hasler refused to speculate on whether his team could still win the minor premiership.

"It's something we haven't spoken about at length," Hasler said.

"I still think to be thinking minor premiership, anyone, it would be crazy. There's still five games of footy to go.

"Five weeks is still a lot of football and a side's fortunes and destiny can change a lot."

Manly host Melbourne in the second last round before finishing off away to Brisbane, another current top-four team.

The notoriously cagey coach was predictably wary about the potential threat posed by the lowly Roosters.

"They're a real threat. They're a quality side," Hasler said.

"The brand of footy they are playing, they are tossing it around, they are throwing it from side to side, they are playing that lateral footy, you have to be on your guard."

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