Manly's backline stocks are looking a little thin just one game into the competition with fullback Brett Stewart joining former Tests winger David Williams on the sidelines.

Stewart suffered a suspected medial meniscus tear in his left knee after putting his body on the line to stop a rampaging Lote Tuqiri in the dying stages of Wests Tigers' dramatic 26-22 win over the Sea Eagles on Monday night.

The Sea Eagles No.1 lay prone after making the crucial tackle on Tuqiri before being carried off by Manly medical staff.

He will undergo scans on Tuesday, though the initial prognosis had him out for up to six weeks.

It was initially feared that Stewart had re-injured the right knee he had surgically repaired last year before Sea Eagles doctor Paul Bloomfield confirmed it was his left knee.

"It's completely unrelated to anything else before," Bloomfield said.

"It may well be a medial meniscus tear but we will know tomorrow when we have an MRI scan.

"It could be anywhere between three and six weeks. It shouldn't be (a season-ending injury) but we'll have to look at the MRI." Williams failed to even make it to round one after going down on match eve, when he suffered a dislocated collarbone at training.

The powerful winger is expected to be sidelined between six to eight weeks.

Winger Michael Robertson, who looms as a possible replacement in the No.1 jumper - said he was hopeful Stewart would not be out too long.

"Brett just can't take a trick at the moment," Robertson said.

"To lose someone the calibre of Brett is going to be a massive blow but someone's going to have to fill in.

"He missed a lot of games last year. He's a freak and you don't want to lose one of your best players.

"It's something we're going to have to deal with." Compounding the Sea Eagles woes, George Rose, Brent Kite and Keiran Foran were all placed on report for high tackles.

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