The headhunter appointed by Adidas to find a new chief executive for the German sportswear firm has approached potential candidates at rivals including Nike, Puma and Amer Sports , a magazine reported on Thursday.

The board of Adidas said in February it had launched a formal search for a successor to Herbert Hainer, who has been in the job since 2001 and faced criticism last year as Adidas lost more ground to Nike.

Without citing its sources, Germany's Spiegel magazine said headhunters Egon Zehnder had approached Puma Chief Executive Bjorn Gulden, who used to work at Adidas, as well as Amer Sports chief Heikki Takala and an unidentified manager from Nike.

An Adidas spokeswoman reiterated the search process was ongoing and the board was looking both inside and outside the group, noting it was a "long-term process" with Hainer's contract running until 2017.

A Puma spokesman declined to comment. Amer Sports was not immediately available to comment.

Puma's Gulden, who only took over in 2013, said last week he wanted to keep doing his current job as long as possible.

In September, a German magazine said Henkel boss Kasper Rorsted was no longer in the frame for the job after holding talks with Adidas.

Global brand chief Eric Liedtke and sales boss Roland Auschel are seen as the leading internal candidates. Adidas said last week it had extended Auschel's contract, due to end in 2017, to 2019.

Some shareholders have expressed a preference for an external candidate, given the problems the company has faced in recent years under Hainer, such as its struggling golf business and its difficulty denting Nike's dominance in North America.

However, Credit Suisse analyst Simon Irwin said he believed the FIFA corruption scandal had tainted the reputation of key sponsors such as Adidas and was making it harder to attract an external candidate.

"We now believe that an internal candidate is much more likely," Irwin said. "This reduces the chance of adopting a more margin-friendly strategy in our view."