The company, whose products include Rennie indigestion tablets and Sanatogen, had been expected to be among a raft of clients moving to JWT following the successful bid by the network's WPP parent for Cordiant, which owns Bates.
This now seems less certain after reports that at least one major network has put together a team after being asked to pitch for the business by Roche chiefs.
The news will be a blow to the senior agency executives assigned to manage the smooth transfer of accounts between Bates and JWT and who are due to meet Roche representatives next week.
Sir Martin Sorrell, the WPP group chief executive, has been striving to reassure major Bates clients. In particular, WPP has been keen to make certain the clients move in with minimum disruption by allowing key Bates account people to move with the business.
Tony Taylor, the Bates board director on Roche, which bills £8 million in the UK, is among an eight-strong Bates team due to transfer with it into JWT.
Bates sources remain convinced Roche won't go elsewhere, having recently had to consolidate all its over-the-counter business outside the US into Bates following the closure of D'Arcy.
Roche, headquartered in Basle,refused to comment on the reports as Campaign went to press.