Mustafi completed a £35m move to the Gunners last week and is in line to make his Premier League debut against Southampton this weekend.
"Mustafi is a player I like," Monreal told the club's official website.
"He has played for Valencia in Spain for the last three or four years, showing impressive from throughout.
"He is very experienced and really tough to beat, which makes him very suitable for the Premier League's style.
"Luckily for him he will feel at home here from the very first day."