Moses Itauma vowed "I'll be back" after the Briton fell short in his bid to become the second-youngest heavyweight world boxing champion after Mike Tyson.
The 21-year-old suffered a ninth-round stoppage to Filip Hrgovic of Croatia in a bruising battle for the vacant IBF heavyweight crown at London's O2 Arena on Saturday.
Itauma has been touted in Britain as the next heavyweight sensation and he dominated much of the fight before running alarmingly out of gas.
It was his first defeat, in his 15th bout, having ploughed his way through the division until that point.
"Yesterday it wasn't my night," Itauma, who was born in Slovakia, said on social media on Sunday after a brief stay in hospital, having been stretchered out of the ring.
"We attempted greatness and just fell short to the more experienced man."
Itauma congratulated the 34-year-old Hrgovic on his surprise victory, the older fighter having used all his ring nous to pull through in a thrilling contest.
"Although I never reached my desired outcome I believe I gained experience that I'll take to my future fights," Itauma said.
"God bless, take care and I'll be back."