The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
Priestland suffered an Achilles injury during his side's 22-16 home defeat to Exeter Chiefs and is now set for a scan.
Welsh prop Samson Lee and lock Aaron Shingler also left the field early to deepen Warren Gatland's woes.
Priestland was Wales' regular fly-half during their Grand Slam win earlier this year, and has 22 caps to his name.
Shingler started the final autumn international against Australia, while Lee has so far been restricted to the bench but becomes Gatland's fifth injury in the tight-head prop position.
And Scarlets head coach Simon Easterby admitted the injuries to Priestland and Shingler are of particular concern.
"He has got an Achilles injury," said Easterby of Priestland.
"We won't know the extent of that until he has a scan but it doesn't look good.
"Aaron Shingler suffered a groin injury and he's been carrying that for a couple of weeks.
"Hopefully he will come through but that didn't look great either."
Easterby was far from happy with his team's performance in allowing Exeter to end their Pool 5 hopes and dump them from the competition.
He said: "You can't give any side the start they had and we slipped off a couple of tackles, and they scored a soft try and a couple of points from our error and indiscipline."
George North, Leigh Halfpenny, Jamie Roberts and Adam Jones are among Gatland's more high-profile injury victims ahead of Wales' RBS 6 Nations opener against Ireland on February 2.