The 12-cap front-rower suffered the injury during the RBS 6 Nations and had an operation to repair a tendon following the summer tour of New Zealand.
It had initially been thought the 24-year-old would have a chance of making Wales Under Armour Series Tests against Australia, Argentina, Japan and South Africa.
But Scarlets head coach Wayne Pivac has confirmed Evans will not be available to play until December, with the west Wales region signing Luke Garrett from the Newport Gwent Dragons as loan cover.
“Luke has been training with us for the last week or so; obviously Rob Evans has had a long-term injury with his surgery and he is not due back until some time in December,” said Pivac.
The Scarlets have other front-row injury concerns with Samson Lee currently sidelined and Dylan Evans struggling to make Friday’s Guinness PRO12 clash with Edinburgh with a shoulder problem.
“Dylan picked up a niggle against Munster and is a bit of a doubt for Friday,” added Pivac. We also have had an injury to Wales Under 20 prop Rhys Fawcett, who we were bringing through the ranks. He has a broken bone in his foot.
“Luke Garrett is there as an insurance policy for us and he did well in a run-out against Bristol the other week. We are pleased to have him on board.”
