The deputy leader of Ukip, Margot Parker, has quit her post in protest at Henry Bolton's refusal to step down, it has been reported.
Parker said Bolton should go "sooner rather than later" as he was leaving the party "in a limbo situation."
Ukip's ruling executive backed a motion of no confidence in the party leader on Sunday (January 21), a week after it emerged his girlfriend had sent racist messages about Meghan Markle.
Bolton has faced a stream of calls to resign since the highly offensive messages sent by Jo Marney were published by the Mail on Sunday.
Parker told the BBC that Bolton's personal life "took over the job he was elected to do" and urged him to stand aside.
She said: "It would be quicker and cleaner if he came to the conclusion he could go sooner rather than later.
"This is taking time away from doing the job. This puts the party in a limbo situation."
The East Midlands MEP will continue her role in the European Parliament, the BBC said.
Party members will now decide Bolton's fate in a vote at an emergency meeting in February.