Best was unable to return for the second half of Sunday's 32-12 defeat of Canberra, the reigning wooden spooners' fourth win from five games this year.
At full-time, first-year coach Justin Holbrook said Best was lucky to have made it that far into the game.
"He wasn't good early on, but he got through to halftime and that was big for us," the coach said.
Best has since been diagnosed with a moderate-grade groin strain, so joins high-profile teammates Kalyn Ponga and Dylan Brown on the sidelines.
Should he require the full four weeks to recover, the former NSW centre will miss clashes against Wests Tigers, the Sydney Roosters, Penrith and South Sydney.
His injury cleared the way for Wilson de Courcey to make his NRL debut on Sunday, and the 20-year-old looms as the likeliest man to join the starting side against the Tigers on Sunday.
Asu Kepaoa and Kyle McCarthy are other options to come into the backline for a clash of two of the NRL's most improved sides.
Brown is expected back from his knee injury in round seven, with Ponga slated for a round-10 return.
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