The Borussia Dortmund man believes his side cannot count on a place in the quarter-finals of the Champions League just yet as the Brazilian prepares to visit Germany with Zenit
Jurgen Klopp's men hold a 4-2 advantage over the Russian side in the last 16 of the Champions League going into this week's home leg.
However, the Germany international feels that the tie is far from over and has warned that the Brazilian could yet swing the odds in Zenit's favour.
"The return game will be hard work," he told Der Westen.
"Zenit have spent a lot of money and we must not take them lightly. Hulk is a physically strong player and you can't take him down easily.
"He can shoot from anywhere, but we're in a good position from the first leg."
Meanwhile, attacking midfielder Jonas Hofmann is optimistic about his side's chances of reaching the last eight, but is still refusing to take qualification for granted.
"Right now, we have one foot in the quarter-finals," he added.
"But 3-0 would be enough for Zenit. This may sound crazy, but we were also 2-0 up out of nowhere in St Petersburg."