Irish referee Alain Rolland dismissed the 22-year-old flanker for a dangerous tackle on winger Vincent Clerc in the 18th minute.
"I'm obviously gutted, but there was no malicious intent," said Warburton.
"I felt like as soon as it hit him his bodyweight took control of what happened.
"I thought it was a normal tackle, next thing I was walking off into the stands."
Warburton is now expected to miss Wales's match against either Australia or New Zealand next weekend.