The Secretary of State for Scotland, Alister Jack, is self-isolating after he developed coronavirus symptoms.
Mr Jack is said to be experiencing "mild" symptoms, including a cough and a temperature, but had not been tested for Covid-19.
He said in a statement: "In the past 24 hours, I have developed mild symptoms associated with coronavirus.
Mr Jack added: "In line with medical guidance, I am self-isolating and working from home."
The Conservative MP for Dumfries and Galloway has been at home in his constituency since Wednesday night.
During the day on Wednesday, Mr Jack was on the front bench in the House of Commons chamber with Prime Minister Boris Johnson on one side and UK government's Health Secretary Matt Hancock on the other.
Both Mr Johnson and Mr Hancock announced on Friday that they had tested positive for Covid-19 and were self-isolating.
With three cabinet ministers now in self-isolation, some have questioned how well those who work in Westminster have been observing social distancing.
The former Cabinet Secretary Lord O'Donnell said politicians needed to "obey their own rules" around social distancing "much more strictly".
Chancellor Rishi Sunak was with the prime minister shortly before he tested positive and England's Chief Medical Officer, Prof Chris Whitty, has also shown symptoms.
Cabinet Secretary Sir Mark Sedwill was also with Mr Johnson, Mr Hancock and Prof Whitty at a Cabinet meeting on Tuesday.
Neither the Chancellor nor Sir Mark had displayed symptoms by Friday night so they had not been tested and were not in isolation.