The league was suspended in March due to the Covid-19 pandemic and will resume on 17 June at stadiums closed to spectators.
“You’re going to get players coming into form that haven’t been in form all season or low in confidence and then suddenly thriving,” Foster, 37, told The Guardian.
“I know for a fact that there are players that do feel massive pressure when they know they have 30-, 40-, 50,000 people watching them.
“You can just see it getting into their head. Not having the crowd there will, without doubt, benefit some people.”
Watford defeated Championship side Brentford 2-0 in a friendly at Vicarage Road on Saturday, a game in which artificial crowd noise was piped into the stadium.
“It really annoyed me,” said Foster, who signed a new two-year contract with the club earlier this week.
“You can only play it at certain times, like when the ball goes out, when it would just come on and be really annoying.”
Watford, who are 17th and above the relegation zone on goal difference, will restart their campaign at home to Leicester City on June 20.