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.
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 was 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.''
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 was 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.''
