The 26-year-old, who joined Widnes from Wigan in 2012, will await a decision on whether he now requires an operation.
Marsh signed a new two-year-deal in April to remain at the club until 2018.
Head coach Denis Betts told the club website: "We're assessing him this week but the early signs mean he will definitely miss the rest of this year."
Widnes Vikings centre Stefan Marsh will miss the rest of the season due to a knee injury picked up in last week's victory over Wigan Warriors.