It is understood the brand wants to reposition its food-on-the-go offering and is looking for a specialist digital agency.
A number of agencies will pitch next week. A decision is expected before Christmas.
Greggs is currently targeting customers who pick up food to consume while out and about, moving away from take-home food.
The chain's food offering is being redeveloped and Gregg's has refurbished hundreds of outlets to appeal to the food-on-the-go market, said the retailer's chairman, Ian Durant, in its annual financial report earlier this year.
In January last year, Greggs launched its first TV campaign in two years. The ads were created by Gratterpalm, with media planning and buying by Carat.
Greggs has not commented on the pitch.