Berlin, Jul 20 (IANS): The mood in Borussia Dortmund's pre-season training camp in Switzerland couldn't be more gloomy.

Only hours after a new arrival, forward Sebastien Haller had been diagnosed with testicular tumour, with the striker leaving for further surgery in Germany, scheduled training sessions took place with lot of worries.

In an official statement, the Black and Yellows announced late on Monday night that the 28-year-old first complained of feeling unwell before training on Monday morning. "He reported he was not feeling well and he had symptoms," head coach Edin Terzic said.

This explains why Haller didn't attend the team's friendly against the Spanish side Valencia (3-1) in Altach in Austria near the Swiss border, Terzic added.

The tumour was found during a medical examination in the team hotel, with Haller returning to Germany to undergo further testing.

"This news today came as a shock to Sebastien Haller and everyone else," the club's sporting director, Sebastian Kehl, stated.

"The entire BVB family hopes that Sebastien makes a full recovery as soon as possible and that we can give him a hug again soon. We'll do everything in our power to ensure that he receives the best possible treatment."

Haller joined Borussia earlier this month from Ajax, with Dortmund paying 31 million euros for a player they targeted to replace Erling Haaland, reports Xinhua.

The France-born Cote d'Ivoire international scored 34 goals for the Dutch side of Ajax last season, including 11 in eight Champions League games.

Haller in several interviews had spoken about his goal to help his new club return to success.

His former clubs such as West Ham and Ajax said in social media postings that they are shocked and hope for a quick recovery.