Sir Keir Starmer is in self-isolation after a member of his family showed signs of coronavirus symptoms, a spokesperson has confirmed.
It means the Labour leader will miss a key Brexit debate on Monday and could be forced to skip Prime Minister's Questions on Wednesday.
The family member with Covid-19 symptoms has been tested and Sir Keir must remain in isolation at least until the result is confirmed.
“This morning, Keir Starmer was advised to self isolate after a member of his household showed possible symptoms of the coronavirus," a statement from his spokesperson said.
"The member of his household has now had a test. In line with NHS guidelines, Keir will self-isolate while awaiting the results of the test and further advice from medical professionals.”
Sir Keir, who isn't showing symptoms himself, was informed of the isolation advice after a studio interview on LBC in which he criticised Boris Johnson's latest Brexit proposal which will be debated in the House of Commons on Monday.
He urged Mr Johnson to reconsider the Internal Markets Bill, which will override aspects of the Brexit Withdrawal Agreement which was signed by both the EU and UK in October.
"He is making a mistake reneging on a treaty, that will have reputational damage for the UK," Sir Keir told LBC radio.
"Here we are on the world stage for the first time in many years on our own and what's the first thing we do? We break a treaty.
"It's basic stuff - if you say to other nations we agree something and a few months later you say no we don't, the chances are they aren't going to trust you going forward."