Cardiff Blues winger Owen Lane has been released from Wales' Guinness Six Nations squad following a "significant" hamstring injury sustained in training.
Six Nations champions Wales will open their defence against Italy at the Principality Stadium on February 1 under new head coach Wayne Pivac.
In a statement the Welsh Rugby Union said: "Further assessments (of Lane's injury) will be concluded early next week to establish an accurate prognosis."
Lane, 21, has two international caps, scoring a try on his debut against Ireland during August 2019.
Liam Williams is still not fit, having been out of action since suffering an ankle injury in the World Cup in Japan.
However, it is expected 18-year-old Gloucester wing Louis Rees-Zammit will be available for the second game of the tournament against Ireland.
The teenager went off injured during his side's Champions Cup defeat against Toulouse on Sunday.
However, Pivac revealed Rees-Zammit should return when Wales travel to Dublin for the fixture on February 8.
Warren Gatland ended his 12-year tenure following Wales' World Cup semi-final defeat against South Africa, with Pivac taking over.