Wales must complete the first three rounds of the Six Nations without Taulupe Faletau after the veteran number 8 was ruled out by a calf problem.
Faletau will miss the games against England, France and Scotland with the injury sustained in Cardiff's 33-22 defeat at Ospreys on 1 January.
Ireland host Wales in round four on 6 March.
The 35-year-old, who missed the autumn because of a knee issue, is not expected to be back in action until late February.
"It’s not clear on his return but we’re definitely looking at the middle of the Six Nations," Cardiff coach Corniel van Zyl said.
Wales are already missing captain Jac Morgan and centre Max Llewellyn for a large chunk of the tournament.
Head coach Steve Tandy names his Six Nations squad on 20 January.
Meanwhile, England's Fin Smith (above) could be a doubt for the game against Wales on 7 February because of a calf injury.
Smith was withdrawn from the Northampton side that fell to a 50-28 Champions Cup defeat at Bordeaux on Sunday just hours before kick-off and is waiting for the results of a scan that will outline a timeframe for his return.
Saints director of rugby Phil Dowson has revealed the British and Irish Lions fly-half will be out for at least a fortnight, leaving Steve Borthwick sweating on his fitness for the visit of Wales.
George Ford started three of England’s four Tests in the autumn but Smith was given the number 10 jersey against Fiji and was on the bench for the opener against Australia.
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