Former Wales and British and Irish Lions captain Sam Warburton says he knew it was time to retire when he realised he would not be able to play at an international standard again.

The 29-year-old announced last month that he was hanging up his boots after failing to overcome neck and knee injuries.

Flanker Warburton, who led the Lions on tours to Australia in 2013 and New Zealand last summer, had not played since the drawn third All Blacks Test 12 months ago and could not regain his fitness during pre-season training with Cardiff Blues.

"I remember saying to the physio, 'I'm fine but when I tackle or run, that's when I get pain,"' Warburton told the Times. "He was like, 'that is a bit of a problem doing what you do.' "

"When I was doing overhead press in the gym, I was still getting nervy symptoms, pain in my neck, and I hadn't even done any contact work. After a week I was coming home from training and I was having joint pain - you can deal with muscle soreness but this was different.

"I didn't want to be that player who was just hanging on, holding a pad. If I couldn't get to the heights I wanted to, I'd rather just call it a day.

"If I couldn't get to an international standard, I was not going to do it and I could tell I wasn't going to make that after about a week's training. My body just couldn't cope with the volume of running any more."

Warburton admits that next year's World Cup in Japan made his decision to quit more difficult.

"We finished our session and we were in a huddle. Some of the senior players and coaches were talking and I remember not being as focused as I should have been, looking at the grass," he added.

"I was just thinking, 'This is it. I have found that session so hard, what with all the changing of direction. My knees are so sore'. I just thought, 'I am never going to get through 14 months to get to the World Cup'."