The Italy international, who was the top scorer in Serie A last season with Torino, made his Bundesliga debut on Saturday but failed to impress in a shock 2-0 defeat for BVB at home to Bayer Leverkusen.
Hamann argues that, while Immobile is by no means a poor player, the 24-year-old striker is ill-suited to Jurgen Klopp's counterattacking tactics.
"I'm not sure if he has very much value for Borussia," the former Germany international told Sky.
"He's a box player and, given the way Dortmund play, I don't know if he helps them."
Immobile, who has been capped four times by his country, netted 22 times in 33 appearances in Serie A last season.