The coveted Pole has already made his feelings clear that he expects to move to Bayern Munich next season, but Watzke has denied having given the striker his word that he can move.
With a switch within the Bundesliga ruled out until his contract expires in 2014, speculation had mounted that he would instead be tempted by a move abroad.
Spain and England had both been rumoured as destinations, with Real Madrid, Chelsea and Manchester City most strongly linked with the 24-year-old.
But Watzke says they too would be wasting their time trying to lure him away from Westphalia.
"Robert will definitely be playing for Borussia Dortmund next season," he told Germany's Suddeutsche Zeitung newspaper. "We need this security to be able to plan (for the season)."
Lewandowski has scored 54 goals in 98 Bundesliga appearances for Dortmund and became the first player to score four goals in a semi-final of the Champions League when he single-handedly dismantled Real Madrid.