Ukip's biggest financial backer has branded the party leader "weak".
Business tycoon Arron Banks told The Independent Paul Nuttall was "weak but potentially a good leader".
Mr Banks was critical of Mr Nuttall's failed campaign in the Stoke by-election.
"You only need to look at Nuttall's campaign, with the stuff on his website and everything. If you were starting a by-election campaign, the first thing you do is check all your stuff."
Mr Banks said he would "definitely" stand against Ukip's only MP, Douglas Carswell, and claimed the party was run like a squash club.
He suggested he could try to force Mr Carswell, who has denied claims he wants to rejoin the Tories, to face a by-election before the expected 2020 general election.
"One of the things Douglas Carswell was very strong on was recall of MPs. Carswell said that if enough of the constituents voted for it, then their MP should be recalled and they would have to face a second election.
"So, if he's really going back to the Tories, as people say he is, one of the things I'm looking at is going to the Electoral Reform Society and saying, 'Let's have a recall'.
"Even though it's not legally binding, we might approach the voters of Clacton and say, 'Look, for these reasons we think Douglas Carswell should be recalled'. And that would be a neat idea, because it would be using his own idea against him."
Mr Banks called for major changes in Ukip, saying: "It needs to be fit for purpose now. It's run like a squash club committee and that needs to stop."