Rafael Nadal didn't retire in Melbourne after getting injured but continued to play finishing off the match as he usually does.
Rafael Nadal has a very principled approach to tennis and generally doesn't retire from matches unless he absolutely must. The Australian Open earlier this year was a prime example of that as he kept playing injured even though there was no way for him to win the match so severely hampered.
The explanation given after the match was typical of Nadal. He felt that retiring as a defending champion is not admirable so he toughed it out and finished the match. It was unwise according to former player Rennae Stubbs who feels like he did more damage to the hip by doing that instead of simply giving up the moment he realized something was wrong.
Sad news on Rafael Nadal having to pull out of the French. I was sitting court-side when he sustained the injury in OZ & I can't believe he kept trying to play. Looking back in hindsight might not have been the wisest to keep playing that match? Just sucks not to have him in Paris.
The take was a rather reactionary one coming down immediately after Nadal admitted he is not ready to play at Roland Garros. Even so, it's a very valid point because hip injuries can be career-threatening and if would have been better for Nadal to not play on an injured hip.
He didn't know the nature of the injury when it happened and continuing is what he generally does. An abdominal tear at Wimbledon last year didn't force him to retire either as he kept battling Fritz and eventually winning the match even though he knew that he would not play in the next one. That's just why he's called the warrior.