Scarlets will again be without British and Irish Lions centre Jonathan Davies for the Pro14 game at home to Leinster on Saturday, 8 September.
Davies was a late withdrawal before last weekend's opening 15-13 loss at Ulster with a hamstring problem.
Outside-half Rhys Patchell is also likely to be ruled out after suffering a head injury.
Scarlets are hoping Wales players Leigh Halfpenny, Hadleigh Parkes, Samson Lee and Jake Ball will return.
Davies has not played a competitive match since suffering a serious foot injury last November while playing for Wales against Australia.
The 30-year-old figured against Bath in a pre-season friendly last month but did not start against Ulster.
"This is unfortunate for Jon, he is such a finely tuned athlete, he is in great shape and itching to go," said Scarlets head coach Wayne Pivac.
"He has felt a hamstring before Ulster and has a little niggle, so it is something at this stage of the season you do not risk."
Pivac says they will treat Davies cautiously after his long-term absence.
"We have to be smart on these things," said Pivac.
"He has a lot of rugby ahead of him and we are only into week two.
"I don't think it is going to be long-term. It will be a week-by-week basis but we won't push him and will get him 100% right.
"It is important with the sort of injury he had last year that the volume he is getting in training is right. He has been out for some time so we have to be mindful of that."
Outside-half Patchell is undergoing return to play tests after his head injury against Ulster and is unlikely to feature against Leinster.
Scarlets will be hoping Patchell's understudy Dan Jones is fit after the young fly-half limped off with a hip injury in Belfast. The region's other recognised 10, Angus O'Brien, is also currently injured.
Wales quartet Halfpenny (groin), Parkes (broken finger), Lee (cheekbone) and Ball (shoulder) missed the season opener through injury, alongside Paul Asquith and Johnny McNicholl.
Pivac hopes the six players will return for the visit of the Pro14 and European champions Leinster after being without 14 of his squad for the Ulster defeat.
If Patchell and Jones are both unfit, Parkes, Asquith, Sam Hidalgo-Clyne and Clayton Blommetjies will be left to cover the outside-half position.