Full-back Davies picked up a knee injury in the 20-16 defeat to the Blues on Wednesday while Thomas is out of the reckoning with back trouble. The match at the Racecourse Ground in Wrexham will be the Scarlets' third outing in eight days but director of rugby Gareth Jenkins believes his squad will be able to cope.
"We've been able to balance our selection so hopefully we won't be affected too much by the injuries," he said. "We've taken a few casualties and that might pressurise our selection, but we knew this was in front of us and we were quite clear about what this week meant."
Connacht beat the Blues at home in their first game of the season, but will arrive in North Wales on the back of a 34-3 defeat to Edinburgh Gunners.
"They'll be resilient and tough, and will make life really awkward for us," added Jenkins. "They will probably be fresh and they are always capable of tripping sides up."
Nearly 40 players were involved in the first Wales Under 18 training session of the season. WRU National Performance Manager Gethin Watts is excited at the potential shown by the group and expects the Regional Under 18 Championship to hone their skills even further.