Earlier this week, Jamie Lomas was accused of kissing carer Katie Moores in his hotel suite after a night out.
"Now that one person has come forward, Kym's worried that the floodgates will open and more will come crawling out of the woodwork. Kym and Jamie are managing to put on a brave face in public," a source told The Mirror.
"But she is telling her mates she fears it will only be a matter of time before more girls try to cash in by claiming they've also had flings with Jamie.
"Jamie's been away in LA with his mates and he has been partying quite a lot. Nobody recognises him out there, unlike here, where he's likely to be caught out on anything he does."
Marsh, who plays Michelle Connor in Corrie, was recently forced to deny claims that she had been abandoned by Lomas as he looked for work in LA.