Three-tour Lion Williams was the shock omission from Wales' 28-man squad. But Howley, who has lined-up alongside Williams for club, country and the famous tourists, has backed the Test veteran to bounce back.
"Having played with him and coached him, I know Martyn will be determined to prove there is life in Martyn Williams," said Howley.
"He will react only positively. He's still a great player.
"He's going to be disappointed. But we've all been through that process when you get to 30-plus. You start looking over those shoulders at the young bucks coming through.
"That's been the case in the back row for a couple of years now with Sam Warburton developing as a player, while now we have seen the emergence of Josh Turnbull.
"But we know what Martyn Williams can do and bring to the party. By no means is he out of the picture.
"The Six Nations gives us the chance to look at one guy who is in form, who is playing for the Scarlets, who deserves his place, while another in Sam who has been playing particularly well for the Blues.
"We just want to see how the young bucks go. But I expect Martyn to come back fighting, as any quality, world-class international flanker would."
Wales head coach Warren Gatland echoed Howley's sentiments.
"There's always a chance for Martyn," added Gatland.
"I spoke to Martyn on the phone before the squad was announced. We knew what a quality player he is, and has been, a great servant to Wales."