With the Bundesliga season kicking off on Friday, August 5th and Dortmund facing Bayer Leverkusen on Saturday, Watzke said the club would need to shop around for another forward soon as all the pressure would be on teenager Youssoufa Moukoko (17).
"Obviously it is clear that his (Haller's) absence will be relatively long and to put everything on Youssoufa Moukoko's shoulders now - he is 17 - would be a bit too much," Watzke told ARD's Sportschau programme.
"So I think that we will be doing something on the personnel level. Although a right solution is also difficult because the market offers are not ample," he said.
Haller was signed last month from Ajax, where he scored an impressive 32 goals in 50 appearances, to replace Erling Haaland, who joined Manchester City. But less than two weeks later and during Dortmund's training camp a malignant testicular tumour was discovered.
The Ivory Coast international underwent surgery in late July 2022 and will now need chemotherapy, being sidelined indefinitely.
Dortmund, who finished runners-up to Bayern Munich in the Bundesliga last season, are also competing in the Champions League group stage.
"Ideally something should happen in the next eight to 10 days," Watzke said on the timing of a possible transfer.
