During an open Q&A session with Twitter followers under the hashtag #askboris, Johnson described himself as a "mega Clarkson fan".
He added that he'd "def let his name go forward" to replace the presenter, who has been suspended by the BBC following a "fracas" over a steak.
...and on that bombshell, I'll be back for another #askboris very soon. Thanks for taking part.Boris Johnson (@MayorofLondon) March 23, 2015
Johnson has in the past been a major advocate of the outspoken Top Gear presenter, calling him a "great man" and saying that he had the "right idea" to stand for Parliament.
"I see that my old chum Jeremy Clarkson is thinking of standing against Ed Miliband in Doncaster," he wrote in the Telegraph in 2013.
Boris Johnson: Photos of London’s mayor playing paperboy in Times Square
"Right idea, Jezza – wrong seat. I hope fervently that the great man can be persuaded to stand against Cleggers in Sheffield, where his majority (unlike Ed’s) is very frail indeed."
The Mayor of London and Conservative politician also backed Clarkson after he said striking public service workers should be "shot".
Johnson tried to help his chum out of a hole by saying: "What he was trying to say was: 'When you’ve a real need for pension reform, is it really necessary to try to paralyse the country?'"
The mayor has appeared on the programme before as the Star In A Reasonably Priced Car. Perhaps the thought of forgoing the Top Gear test lap was too much to bear.Reuse content