One sales source described the market as "slightly depressed" but "not horrific" as broadcasters seek "late money".
ITV has already warned that its revenues will be down by 5-10% in September compared with a year ago, when the Rugby World Cup gave it a fillip. However, Channel 4 is hoping its Paralympics coverage will shore up ad revenues.
Media buyers have differing views. Some say October could be down by as much as 10%, but others believe it will decline only slightly.
October and November are crucial months for broadcasters, when retailers launch their biggest campaigns of the year in the run-up to Christmas.
Before the Brexit result, forecasters had expected the TV market to be up 5% this year. It is now likely to be flat.
