Commons Leader Mark Spencer has said it is up to Andrea Jenkyns to “justify” her actions after she was caught on camera appearing to make a rude gesture while entering Downing Street.
The Tory MP made the sign with her hand as she walked through the black gates, prior to being named education minister.
Mr Spencer, a former chief whip, said he does not believe the gesture was “the right thing to do at all”.
Asked if it is acceptable, he told BBC Breakfast: “No, I don’t think it is, to be honest. I don’t seek to condone that at all.
“I mean, Andrea will have to… justify that for herself. But I do understand emotions were running pretty high and they were pretty raw on that day. But I don’t think that was the right thing to do at all.”
Pressed on whether she should retain her ministerial role, he said: “That’s not my decision.”
Ms Jenkyns was appointed to the role of parliamentary under-secretary of state at the Department for Education on Friday in a reshuffle by Prime Minister Boris Johnson.
The footage, shared on social media on Thursday evening, appears to have been filmed shortly before Mr Johnson announced he was stepping down as leader of the Conservative Party.
It is unclear who the gesture was aimed at.
In response to the video, shadow education secretary Bridget Phillipson tweeted: “Ministers aren’t expected to be perfect. But is it really too much to ask that they don’t treat the public like this?”
Ms Jenkyns and the Department for Education have been contacted for comment.
The education minister was one of the MPs to show support for Mr Johnson outside No 10 on Thursday as he announced his resignation.
A timetable for the Conservative Party leadership contest is expected to be drawn up next week after the election to the executive of the backbench 1922 Committee.