Borussia Dortmund striker Sebastien Haller will be out of action for at least "several months" after surgery on a testicular tumour, the Bundesliga club said on Wednesday.

The Ivory Coast attacker was diagnosed last week during the team's pre-season training camp in Switzerland.

"He had a successful operation last week," said Dortmund sporting director Sebastian Kehl.

"He will definitely be out for a few months.

"The operation went very, very well and he's on the right track."

Dortmund paid Ajax 31 million euros ($31.5 million) for the 28-year-old earlier in the close season after he scored 47 goals in 65 appearances for the Dutch side.

The club have not said if they will look for a short-term option to boost their attacking options in the absence of Haller, who was signed as a replacement for Erling Haaland after the Norwegian's departure for Manchester City.

Dortmund start their season on Friday with a German Cup game at 1860 Munich.