Though neither company would comment, Emap is widely expected to announce plans to attach one of its magazine titles to the bid.
The news comes at a time when some other potential partners in the bid have expressed concern that 4Radio might be offering spectrum space to more people than it can accommodate.
"It seems as if they might be trying to tie everyone up so that if they then had to leave anyone off the application, it wouldn't give those people enough time to tie up deals with any other bidders," said one.
But Nathalie Schwarz, director of radio at C4, strongly refuted these claims, saying 4Radio was legally obliged to talk to everyone who approached them.
"We're simply doing our job," she said. "We have a very experienced team behind this and they can add up. We haven't yet revealed what we're going to do on the capacity, so who's to say we don't need to talk to a lot of people?
"We have some very innovative things planned."
C4 has been told it could be in line for some extra space from existing digital capacity after the culture secretary, Tessa Jowell, confirmed that the BBC had agreed, in principle, to make available some of its allocated space - enough for a television station and three radio stations - ahead of the digital switchover in 2012.
Speaking in the House of Commons last week, Jowell confirmed she would decide whether to pursue this power when the results of C4's financial review were submitted this summer.
Schwarz this week confirmed that should the spectrum space come C4's way, some of it would be used to broadcast 4Radio.
Emap's move towards a 4Radio partnership comes as the company announces plans for more than 40 job cuts, largely in programming roles, in its local radio network, affecting its Big City Network in Scotland and Northern Ireland.
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