Business Secretary Alok Sharma is self-isolating at home after becoming unwell in Parliament.
Mr Sharma looked uncomfortable while taking part in a debate on Wednesday, mopping his brow several times with his handkerchief while speaking.
A spokesman said the MP for Reading West had been tested for coronavirus and had returned home.
While it is unknown if Mr Sharma has the virus, it has added to the row over virtual proceedings in Parliament.
Earlier this week, MPs voted to return to physical sittings in Parliament - with additional motions due later to allow members who cannot attend due to age and health issues to participate via Zoom and to vote via proxy.
But critics have said the motions do not go far enough, calling it "irresponsible" to return during the outbreak and saying it puts MPs, their families and their constituents at risk.
Labour's shadow leader of the House, Valerie Vaz, said Parliament had been brought into "disrepute" and stopping the so-called hybrid proceedings was "putting people's lives at risk" - calling for virtual measures to be in place until the R number had gone down and the government's alert level had fallen.
But Leader of the House, Jacob Rees-Mogg, said Parliament should "lead by example".
He added: "Across the country people are going back to work. How can we look teachers in our constituency in the eye when we are asking them to go back to work and we are saying we are not willing to?
"We have to be back here delivering on the legislative programme and being held to account."
Liberal Democrat MP Alistair Carmichael is expected to apply for an emergency debate later on how to conduct business in the Commons during the pandemic.
'In line with guidance'
Mr Sharma was pictured in Downing Street on Tuesday, and took part in votes in the Commons later that day.
On Wednesday, he was in the Commons chamber for nearly an hour while leading for the government on the Corporate Insolvency and Governance Bill.
A spokesman for the business secretary said on Wednesday: "Alok Sharma began feeling unwell when in the Chamber delivering the second reading of the Corporate Insolvency and Governance Bill.
"In line with guidance he has been tested for coronavirus and is returning home to self isolate."
It's important to highlight that we don't know for sure whether the business secretary has coronavirus.
However, a potential case is causing real anger at Westminster.
Senior opposition figures say it shows the government was wrong to scrap a hybrid model which allowed MPs to contribute and vote remotely.
There are concerns some MPs didn't maintain social distancing rules in lengthy voting queues. Others fear they could become super spreaders, taking the virus back to their constituencies if there is an outbreak.
If Mr Sharma did test positive, anyone he had spent more than 15 minutes within two metres of would have to self-isolate for two weeks.
During the debate, Mr Sharma's opposite number, shadow business secretary Ed Miliband, passed him a glass of water at one point.
Mr Miliband subsequently sent his best wishes to Mr Sharma for a quick recovery.
The House of Commons authorities said "additional cleaning" had taken place, following the debate.
And the BBC's chief political correspondent Vicki Young said the MP who had sat nearest to Mr Sharma during his statement insisted that social distancing protocols had been observed throughout.
Although it is not yet known if Mr Sharma has contracted coronavirus, if his test comes back positive, the government advice is for his "close contacts" to self-isolate for 14 days.
Those who count as close contacts are either:
- People you spend 15 minutes or more with at a distance of less than 2m
- People you have direct contact with - such as sexual partners, household members or people with whom you have had face-to-face conversations at a distance of less than 1m
Mr Sharma was one of hundreds of MPs who queued around the building on Tuesday at two metre intervals as the Commons introduced new temporary voting procedures.
BBC Newsnight's Nick Watt said talks were at an "advanced stage" to change the temporary system, instead allowing MPs to vote by swiping their parliamentary passes in the normal voting lobbies.
But while it would be quicker than the system used this week - which saw votes take up to 46 minutes - it would not be as fast as the usual system, which sees votes completed in around 15 minutes.
While the number of MPs permitted to sit in the chamber is still limited, many MPs are unhappy about being forced to return to Westminster, saying it poses a risk to them and their constituents.
Others are concerned MPs will be forced to expose the personal situations of them and their families in order to fit the criteria to be allowed to participate virtually.
The SNP's deputy Westminster leader, Kirsty Blackman, said she sent her best wishes to Mr Sharma, but added: "It demonstrates just how ridiculous and irresponsible the Tory government's decision to end virtual participation in Parliament was.
"They must now rectify this serious mistake and reintroduce hybrid proceedings without delay."
But Northern Ireland Secretary Brandon Lewis told BBC Radio 4's Today programme it was "premature" to use Mr Sharma as the case to support keeping virtual proceedings, as his results have not even come back yet.
Labour MP Karl Turner said he had asked the Health and Safety Executive to conduct an urgent risk assessment of working conditions in Parliament.
He said MPs having to "huddle together" on escalators on the parliamentary estate while lining up to vote were among a number of "unsafe practices".
The HSE said it was aware of the letter and would "respond in due course", adding: "While we have no jurisdiction at the Palace of Westminster, all places of work are expected to adhere to the government's working safely guidelines."
There have also been issues in committee rooms, with members not being able to sit around the tables and still keep to social distancing rule.
At the start of the Domestic Abuse Bill Committee, it's chair, Tory MP Peter Bone, said some members were having to sit in the public gallery away from the microphones, meaning they could not be recorded so could not contribute.
The Westminster leader of Plaid Cymru, Liz Saville Roberts - who sits on the committee - called it a "shambles", adding: "Westminster isn't working."