Lewis, 25, had been in sparkling form for the west-Wallians, scored two tries and making one on Judgement Day against Dragons before limping off in the second half at the Cardiff City Stadium.
Confirming the injury on social media platform X, the Scarlets confirmed the time frame and said the player would go under surgery this week.
Head coach Dwayne Peel had suggested the uncapped Lewis had been in contention for Wales’ summer tour of Australia before injury struck.
Speaking about the injury Peel said he was “gutted” for former Wales Under-20 international Lewis.
“He was excellent against the Dragons and I said to our analyst on about 45 minutes, Tomi is playing himself on the tour here.
“But the future is bright for him and he will come back stronger.”
[Lead image: Scarlets Rugby]
