Co-owner Debi Morisot said The Malt Shovel Inn had lost business since maintenance work started at junctions 11 and 12.
The roadworks near Gaydon were due to be finished in April but have been delayed until the summer.
The council said once completed, the maintenance work would prevent future delays in the area.
Ms Morisot runs the pub with her husband and said: "The loss to our trade in the future is unquantifiable."
The couple blames poor signage for the lack of customers.
"It's horrendous - we live here and we get confused," Ms Morisot added.
Peter Butlin, from Warwickshire County Council, said: "We have put up plenty of signage, specifically for the pub involved."
He added there would also be "benefits in the long term" as the work would help ease congestion around the Jaguar Land Rover site entrance at the start and end of day.
The owners of a Warwickshire pub claim they have lost 20% in trade since the M40 roadworks began in August.