"It is a bit ironic how our careers have parallelled," Howley told the South Wales Echo. "But as a forward it is much harder to be at the top of your game than a back.
"Even though he was a marked man for Wales and the British Lions he still managed to go forward. He was a superb rugby player and took a lot of hits over the last years.
"Scott's body has said 'enough is enough' and I wish him all the best in whatever he does in the future."