Leigh Halfpenny, who dislocated his right shoulder against England on Sunday, will undergo surgery tomorrow.
He is expected to be out for up to four months, the WRU says.
Rhys Webb has now been released from the National Squad following his ankle injury, and will be assessed by a medical team at the Ospreys.
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Any heavy showers will clear away northeastwards through late evening.
The Scarlets were comprehensively beaten 38-16 by Leinster in Dublin.
Cardiff Blues survived an onslaught from Pau's powerful pack to book a place in the European Challenge Cup final.