Southampton, West Ham and Sheffield United have also agreed deferrals, while Arsenal's players will take a 12.5% pay cut over the next year.
The Premier League fears a failure to finish the season could cost clubs £1 billion.
"It is a show of unity which we know our supporters and the wider Watford community will appreciate, and shows an awareness of the need for everybody to pull together in these incredibly challenging times," said Watford chairperson and CEO Scott Duxbury.