Nadine Dorries MP has said Michael Fallon's resignation from the Cabinet represents a "massive loss" for the Conservative Party.
The former Defence Secretary left his position in the wake of allegations made against him in a dossier of MPs.
Earlier in the week, he had apologised for repeatedly touching Julia Hartley-Brewer's knee at an event in 2002.
Gavin Williamson, the former Chief Whip, has been appointed as his replacement.
Dorries, the MP for Mid Bedfordshire, said Fallon had been a major asset for the Tories.
She told Julia Hartley-Brewer: "He’s an absolutely huge loss, he's a huge operator for us.
"He was the one who said Ed Miliband had stabbed his brother in the back which got huge political traction for us.
"He’s going to be a massive loss to the Conservative Party, he was one of our most effective secretaries of state.
"We’re operating now as a party where almost 70% of MPs are new intake. We need the experience of people like Michael Fallon."