wing James is expected to be out for a month with a rib injury.
The duo sustained the injuries during the 45-3 Magners League win over Connacht which lifted the Scarlets to the top of the table.
Manu scored two first-half tries in the rout at Stradey Park and his injury has forced Nigel Davies to examine his options in the transfer market.
Team manager Garan Evans said: "We have three fit props in the squad at the moment so we are looking at cover options."
Former All Black Kees Meeuws is the only fit tight-head prop at the region for Friday's match at Edinburgh after Ben Broster and Bruce Douglas left the Scarlets in the summer.
Kiwi centre Regan King is set to feature at Murrayfield after overcoming the hamstring problem that forced him to miss the opening week of the season.