Wales fly-half Rhys Priestland has been ruled out for around six months and will miss the Six Nations.
The Achilles injury he suffered in the Scarlets' Heineken Cup defeat to Exeter last weekend makes him a major doubt for the Lions tour next summer too.
The news is a huge blow for Wales and Lions boss Warren Gatland, as well as his club.
Priestland was expected to be battling it out with Ireland's Jonathan Sexton for the coveted Lions No 10 shirt in Australia.
Scarlets coach Simon Easterby confirmed that Priestland underwent surgery on Tuesday morning.
"I think it was fairly straightforward given that the snap was halfway up his Achilles," said Easterby.
"It used to take nine or 10 months for a player to come back from this injury but some can get back after six months these days.
"Rhys will have his targets and will want to push himself but we must be clear he can't come back before he is ready.
"Unfortunately it means Rhys will miss most of the season which is obviously a big blow for him.
"He had recovered from a couple of poor performances in Wales' early autumn games. He played well against Australia and was playing well for us last weekend before he got injured."
Priestland was a key performer in the Wales team that made it through to the semi-finals of the 2011 World Cup in New Zealand and then helped them to Grand Slam glory earlier this year.
The news of his injury is the latest setback for Howley, who already knew he would be without prop Aaron Jarvis for the entire Six Nations.
Lock Alun-Wyn Jones and flanker Dan Lydiate are set to play only limited parts in the tournament, while full-back Leigh Halfpenny and centre Jamie Roberts face a race against time to be fit.
With winger George North having not played since the defeat to Samoa nearly a month ago due to a hip problem, the interim coach has much to ponder ahead of his team's opening fixture against Ireland on February 2.
With Priestland absent, the number 10 jersey looks to be between Perpignan's James Hook and Dan Biggar of the Ospreys.