Robinson is sidelined due to a three-match suspension imposed following his red card in the derby defeat against Swansea.
There was better news, though, for Hudson with Perry Ng and Mahlon Romeo both returning from injury and featuring in a 1-0 victory over Rotherham on Saturday.
And there is an encouraging progress report on City's Wales international Rubin Colwill, who is nearing a first-team return after being sidelined because of a hip problem.
Watford will head to South Wales chasing a fourth Championship victory from the last five starts.
But Hamza Choudhury is an absentee, serving a suspension after collecting his fifth yellow card.
Hornets boss Slaven Bilic will hope for positive news on Keinan Davis, who missed Watford's last outing at Wigan due to a hip injury.
And Craig Cathcart is another player who could feature following injury as Watford look to keep an impressive recent run of form going.