Andrew Napolitano, the senior legal analyst for Fox News, has been temporarily sidelined following his unproved assertion last week that former President Barack Obama had asked for British assistance in spying on Donald J. Trump, a person briefed on the decision said on Monday.

Mr. Napolitano did not appear on Fox on Monday, even though there were two news events that normally would have called for his services: hearings involving the F.B.I. director James B. Comey, and the Supreme Court nominee Neil M. Gorsuch.

Mr. Comey’s hearing touched on Judge Napolitano’s allegation — which both President Trump and his press secretary, Sean Spicer, repeated — that British intelligence officers wiretapped Mr. Trump at Mr. Obama’s request.

It is not clear how long Mr. Napolitano will be off the air, but his absence from Fox’s airwaves on Monday was an indication that the network was not pleased with the unwanted attention focused on his unfounded allegations.

The Los Angeles Times reported Mr. Napolitano’s absence on Monday. Fox News declined to comment.

Last week, Mr. Napolitano, a former New Jersey Superior Court judge, reported on the morning show “Fox and Friends” that the Obama administration had asked British intelligence to wiretap Mr. Trump during the 2016 presidential campaign.

The claim was forgotten nearly as quickly as it was stated until Mr. Spicer repeated it in a news briefing later in the week. Mr. Trump then brought it up again on Friday, saying, “All we did was quote a very talented legal mind.”

Fox was then put into the awkward position of denouncing Mr. Napolitano’s allegation, with the daytime anchor Shepard Smith saying on Friday: “Fox News cannot confirm Judge Napolitano’s commentary. Fox News knows of no evidence of any kind that the now-president of the United States was surveilled at any time, any way. Full stop.”

During a congressional hearing on Monday, Mr. Comey said there was no evidence that Mr. Obama had wiretapped Mr. Trump. And Adm. Michael S. Rogers, the director of the National Security Agency, said at the same hearing that there was no evidence that the British had been asked to intercept conversations, as Mr. Napolitano had asserted.

It is not known whether Mr. Napolitano’s future at Fox News has been thrown into doubt, or whether network executives are simply trying to remove him from the current news cycle.