However, Moyes has suggested that the Hornets should not be judged on their blip, and has backed Gracia to make an immediate impact at Vicarage Road.
At a press conference, the 54-year-old told reporters: "I think Watford have always been a decent team. Look at the start of the season, the opening three months they were right up there. They had a middle spell where they didn't do as well but they've always been seen as a good side.
"The new manager will be having an impact. I know Javi from Malaga, and I am sure he will. Sometimes, football clubs can change but Watford have had a few managers over the years, they'll know if it works for their club."
Watford currently hold a three-point advantage over the Hammers in the top-flight standings.