BERLIN (Reuters) -Puma Chief Executive Bjorn Gulden is leaving the German sportswear maker at the end of the year to take the helm at rival Adidas (OTC:), according to an industry source.

Puma announced on Friday that it had appointed Chief Commercial Officer Arne Freundt as the new CEO from Jan. 1 after Gulden decided to let his contract expire at the end of the year, but did not say what Gulden's plans were.

Freundt, who has worked for Puma for over 10 years and was promoted to CCO last year, will receive a four-year contract.

Adidas confirmed on Friday that it is in talks with Gulden about possibly replacing Chief Executive Kasper Rorsted.

Adidas has been looking since August for a successor to Rorsted, who plans to leave his post in 2023.

Germany's manager magazin, which first reported the move, said Gulden could not switch directly to Adidas due to a competition clause in his contract, and that Chief Finance Officer Harm Ohlmeyer would likely lead the company in the interim.

Adidas shares were up nearly 20% after the report.

"Bjorn Gulden had a very high reputation as Puma CEO, had been instrumental to the turnaround of the company and Puma's strong brand heat," Stifel analyst Cedric Lecasble said, adding that he could help strengthen the momentum of the Adidas brand.

Problems have been mounting recently at Adidas, which cut its full-year forecast on Oct. 20, citing weaker expectations for China, lower demand in major Western markets and one-off expenses related to its exit from the Russian market.

Adidas also ended its partnership with the artist formerly known as Kanye West last month, which it said would have a "short-term negative impact" of up to 250 million euros on net income this year.

Global credit ratings agency Moody's (NYSE:) downgraded its outlook for Adidas to "negative" from "stable" on Friday.