The Hornets are yet to win a Premier League match this season, and are rock bottom after five defeats and five draws from their opening 10 Premier League fixtures.
Chelsea sit comfortably in fourth place after 10 League matches and are level on points with third placed Leicester City, who are above them on goal difference.
Despite Watford’s poor run of form, the former Derby County coach said it will be very dangerous for his side to be complacent against the hosts.
The Blues were crashed out of the Carabao Cup on Wednesday by Manchester United and Frank Lampard is keen to see Chelsea put the 2-1 defeat behind them.
"I'm very much of the mindset that games become more dangerous with overconfidence," Lampard said in his press conference ahead of Chelsea’s visit Vicarage Road.
"We must understand Watford and their quality.”
"Last season their personnel was similar and they were getting big results, they made the FA Cup final.
"We cannot underestimate a team that will be hurting because they have not won for a while. They will have every ambition to win this game, so I'm even more focused on what we need to do."
Lampard was asked about the availability of Antonio Rudiger, N’Golo Kante and Ross Barkley who have not been playing recently due to injury but the former England midfielder ruled them out.
