In a horror final 15 minutes for the Tigers in Gosford on Saturday night, Luai first limped off with a knee injury in the same set that Souths took a four-point lead.
Then while chasing the game with two minutes to play, Doueihi was left stranded on the far sideline after clutching at his right hamstring.
Both will head for scans, following a match that the Tigers dominated the territorial battle but only scored two tries just before halftime.
The Tigers have cleared Luai of a season-ending ACL rupture, but fear he is still set for a stint on the sidelines.
"It doesn't look good. He's going to get scans obviously. Medical staff say he will be out for a little bit. Hopefully maybe four (weeks)," coach Benji Marshall said.
"(Adam)'s got some tightness in his hamstring. He's had a pretty big week with the load with what he has had to do at No.7.
"He'll get a scan, hopefully it's not too bad."
Even with the loss, Marshall walked away pleased with his side's effort after an ordinary start from which early penalties and errors handed Souths a 12-0 lead.
Where the Tigers' attack was free-flowing last week in their 44-16 win over North Queensland, Marshall insisted the joint-venture had found their blueprint as a side.
The same could not be said for Wayne Bennett, who was highly critical of the Rabbitohs performance in the win.
Bennett offered little praise for the Rabbitohs defence, despite them holding on for 26 consecutive play-the-balls at one stage in the first half.
And he had little praise for their attack, where two key Alex Johnston plays won them the game in the second half.
After trailing 14-12 at the break when Latrell Mitchell gave away an eight-point try for contact on Tigers centre Heamasi Makasini as he scored, Souths took their chances after the break.
Johnston first batted back a Jamie Humphreys bomb for his centre Mitchell to score, before the NRL's greatest every try-scorer broke a 16-16 deadlock when he chased down a Cody Walker grubber.
Jye Gray also had some nice touches, scoring Souths' first down the right edge, throwing a ball for the Rabbitohs second through Jack Wighton moments later.
The fullback also outjumped Tigers fullback Jahream Bula late in the game to claim a bomb, ending one of the joint-venture's last attacking raids.
"Nothing pleased me (about that game)," Bennett said.
"We're better than what we played tonight. If we keep playing like that we won't be in contention for anything except the bottom end of the competition."
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