Sky Sports understands that Dinamo Zagreb striker Duje Cop is attracting interest from clubs across Europe.
Stuttgart followed Mainz out of the DFB-Pokal in the first round, succumbing 2-0 to Bochum, while Marco Reus returned in a victory for Borussia Dortmund.
Christian Gentner is to continue as captain of Stuttgart, the Bundesliga club have confirmed.
Two early goals helped Hull City warm up for the start of the new season with a 2-1 friendly victory at Stuttgart.
Vedad Ibisevic has signed a new deal at Stuttgart, ruling out any possible switch to England.
Chelsea central midfielder Oriol Romeu has joined Bundesliga side Stuttgart on a season-long loan.