Werder are launching a bid for Klaassen, who they see as a replacement for Thomas Delaney, now of Borussia Dortmund.
Stevens told BILD: "His sense of the team is great. He always thinks of the team and never lets them down. He is a team player who always has good moments.
"He often arrived late in the penalty area at Ajax, determined the game and made for many a goal. He is a good player.
"I do not understand why he did not prevail in England. His playing style would definitely fit into the Bundesliga. "
On comparisons with Delaney, Stevens added: "Klaassen is a different guy. I think he's even more mature."