She said she did not believe the Scottish Government would be justified in calling a second independence referendum if it failed to obtain its own deal.
An independent Scotland would be outside the EU and would lose membership not only of the European single market, but also the single market of the United Kingdom, she said.
Her comments came as First Minister Nicola Sturgeon set out her proposals for keeping Scotland in the EU single market and the customs union.
Mrs May was challenged by SNP MP Pete Wishart over the possibility of “differential arrangements” for Scotland as she gave evidence to the cross-party House of Commons Liaison Committee in Westminster.
The Prime Minister told him: “What we will be negotiating is a United Kingdom approach and a United Kingdom relationship with the European Union. I think you’ve assumed an acceptance of differential relationships which I don’t think it’s right to accept.
“I said when I became Prime Minister and first met the First Minister that we will look very seriously at any proposals that come forward from the devolved administrations, but there may be proposals that are impractical.”
She added: “I don’t think there is a need or a reason for the Scottish Government to hold another independence referendum. I think the Scottish people gave their view in the referendum of 2014.
“If Scotland were to become independent, then not only would it no longer be a member of the European Union, it would no longer be a member of the single market of the European Union and it would no longer be a member of the single market of the United Kingdom.
“The single market of the United Kingdom is worth four times as much to Scotland as the single market of the European Union.”
Mrs May said she welcomed the “contribution to the debate” represented by the Scottish administration’s paper, though she said she had not yet had time to read it.
“We’ve been encouraging the devolved administrations to identify their particular concerns and priorities so that we can take that forward as part of the discussions we are having to ensure we have a full UK view as we go into the negotiations,” she said.
“I would expect the Welsh Government and Northern Ireland Assembly to come forward with the particular concerns they have and we will be able to discuss these within the Joint Ministerial Committee (JMC) structures that we have.”
Asked whether powers on issues like agriculture currently held by Brussels could be devolved to Edinburgh after Brexit, the PM said: “We will obviously have discussions within the JMC environment about how the arrangements will work when we have to take a framework currently set out in Brussels into the United Kingdom and recognise the different interests of the devolved administrations and the different devolution deals currently in place.”