The 31-year-old, who arrived at the capital outfit from Barcelona in the summer, has scored three times for the club in the early part of the season.
"He's a top player. He's probably the player who's most used to winning in our squad. He's very important for us; he takes up great positions, is good with the ball and most importantly, scores goals," Simeone told AS.
"What surprises me is the work he puts in for the whole group; that's something I like a lot and which is good for everyone."
Atletico will be without Villa's strike partner Diego Costa for the European clash through suspension.