Deulofeu struck a hat-trick on Friday night as the Hornets thrashed Cardiff City.
"I believed I was the king of the weekend until I saw Messi in the Pizjuán," Deulofeu told El Transistor.
"He is an incredible player, I really enjoy watching him."
On his time with Barca, he also said: "I really enjoyed my time at Barça because I played alongside the best, but I had to look after my own career.
"At Barça I was at home, in the best team in the world, but not feeling important. I'm a person who does not have a lot of patience, I like to play and I wanted to feel important."