Caroline Nokes, who Boris Johnson sacked when he moved into Number 10 last summer, hit out at the appointment publicly on Monday.
The chairwoman of the Commons Women and Equalities Committee and former Immigration Secretary wrote on Twitter: “Cannot believe No 10 has refused to comment on Andrew Sabisky.
“I don’t know him from a bar of soap, but don’t think we’d get on ……. must be no place in Government for the views he’s expressed.”
There are growing calls for Mr Sabisky, 27, to be removed from the government set up after comments he made surfaced – including suggesting enforced contraception to stop unplanned pregnancies creating a “permanent underclass”.
Tory MP William Wragg wrote on Twitter: “Andrew Sabisky’s presence in no.10 is a poor reflection on the Govt and there is no way to defend it. He needs to go. ‘Weirdos’ and ‘misfits’ are all very well, but please can they not gratuitously cause offence.
“I cannot be the only one uncomfortable with recent no.10 trends.”
Mr Sabisky was brought in to Number 10 after Mr Johnson’s chief adviser Dominic Cummings called for “misfits and weirdos” to apply
Other comments reportedly made by Mr Sabisky include suggesting that black Americans have a lower average IQ than white Americans.
And writing on Mr Cummings’ website in 2014, he said: “One way to get around the problems of unplanned pregnancies creating a permanent underclass would be to legally enforce universal uptake of long-term contraception at the onset of puberty.
“Vaccination laws give it a precedent, I would argue.”
Many saw the comments as championing eugenics – or the selective breeding of people.
In a briefing to journalists on Monday morning, a spokesman for Mr Johnson refused to condemn Mr Sabisky’s views and refused to say if the Prime Minister supported the adviser’s opinion on eugenics.
A Number 10 spokesman said: “I’m not going to be commenting on individual appointments.”
The spokesman added: “The Prime Minister’s views on a range of subjects are well publicised and documented.”
Number 10 insiders insisted that Mr Johnson did not support eugenics.
Representatives for the Labour Party and the SNP have criticised Mr Johnson for the move.
Labour Party chairman Ian Lavery said: “It is disgusting that not only has Number 10 failed to condemn Andrew Sabisky’s appalling comments, but also seems to have endorsed the idea that white people are more intelligent than black people.
Scottish First Minister Nicola Sturgeon said the Government must “demonstrate some basic but fundamental values”.
Geneticist and broadcaster Dr Adam Rutherford also criticised the comments, writing on Twitter: “Like Cummings, he appears to be bewitched by science, without having made the effort to understand the areas he is invoking, nor its history.”
It is understood that special advisers are prepared to boycott meetings where Mr Sabisky is present and refuse to reply to any emails he sends.