Claudio Ranieri says it is a "bad moment" for Watford, who have held only one full training session in over two weeks.
The Hornets face West Ham on Tuesday (15:00 GMT) in their first game since a 2-1 defeat at Brentford on 10 December.
Following a Covid-19 outbreak in the squad, their last three games against Burnley, Crystal Palace and Wolves have all been postponed.
Ranieri said trying to arrange training recently has "not been easy".
"I have just today [Monday] had the first training session all together," he said.
"Fortunately today all my players arrived together and that is very, very important.