Michael Phelps, the 23-time Olympic gold medallist, has jokingly challenged UFC champion Conor McGregor to a swimming race.

The American swimmer posed the question on Twitter just three days after McGregor lost his multi-million pound fight against Floyd Mayweather in Las Vegas.

The Irish fighter has yet to respond to Phelps’ invitation but interest around a possible race has already grown with the Olympian’s post being re-Tweeted more than 35,000 times.

Phelps took on his own challenge this summer when he lost in a race against a computer-generated shark.

The 32-year-old lost by two seconds in a Discovery Channel publicity stunt in July.