WWAV, which is believed to handle outdoor spend of around £3m a year, currently has a direct relationship with WPP subsidiary Kinetic.
Major outdoor spenders among WWAV's clients include children's charity the NSPCC, Somerfield supermarkets and financial services company AXA UK.
WWAV also works for Barclays, L'Oreal and the Central Office of Information, which uses the agency to handle briefs for the Home Office, Department of Trade and Industry and Department for Work and Pensions.
Although Kinetic manages the majority of WWAV's outdoor work, the direct marketing agency already uses Posterscope for its client AXA. WWAV works for both AXA PPP Healthcare, the health insurance provider, and AXA UK, the pensions, investments and assurance arm of the Paris-based group.
A spokesman for WWAV said of the agency's relationship with Kinetic: "It is under ongoing review."
Media Week understands that a decision is due within weeks.
Posterscope is owned by Aegis, which like WPP operates rival agencies to Omnicom. However, Omnicom's PHD and its OMD UK Group already have direct relationships with Posterscope.
Posterscope is on a new business drive following the transfer of MediaCom's £90m outdoor business to Kinetic.