Foot op for Wales star Williams
Liam Williams faces a World Cup fitness battle after undergoing foot surgery.
The Scarlets back-three star has been retained in Wales' World Cup camp, but there is no timescale yet on his recovery.
The 24-year-old has become an integral part of coach Warren Gatland's Wales set-up, and would prove a big loss should he fail to beat the problem in time for the World Cup's September kick-off.
A statement from the Welsh Rugby Union (WRU) read: "Liam Williams has undergone surgery on a foot complaint. He will continue his World Cup preparations within the Wales camp."
Williams dislodged wing Alex Cuthbert in Wales' RBS 6 Nations starting line-up, but is equally adept at full-back.
Head coach Gatland will be at pains to allow the 23-cap star as much opportunity to recover as possible, with versatility vital in final 31-man World Cup squads.
Wales must already do without centre Jonathan Davies, who will miss the entire tournament with knee ligament damage.
Wales will open their World Cup account by taking on Uruguay at the Millennium Stadium on September 20, contesting Pool A along with hosts England, Australia and Fiji.
Wales are already into the second week of their early World Cup preparations, at their Vale Resort base near Cardiff.
Kiwi boss Gatland will lead a 15-day training camp in Switzerland, before a trip to Doha, Qatar, that precedes August's warm-up fixtures.
Wales will return to Gatland's favourite haunt of Spala in Poland in the midst of their warm-up matches.
Wales must name their final World Cup 31-man squad on August 31, leaving Williams already watching the clock on his return.