The 20-year old joined Hamburg's youth academy when he was 16 and he has progressed through to the first team, scoring nine goals so far this season.
Agent Thies Bliemeister also revealed that Inter Milan have been keeping tabs on his client, but says they are yet to make a formal bid.
"Inter Milan's emissaries saw a couple of his matches, but so far I have not had any contact with the Italian club's officials," he told Interlive.
"A transfer in the next summer? He has signed a new contract with Hamburg SV extending it for one year, but there have been many offers for him as from Manchester United and Chelsea."