(Reuters) - One of Whole Foods Market Inc's <WFM.O> top ten shareholders has met potential activist investors to discuss management changes at and explore a sale of the upscale grocery chain, Bloomberg reported, citing people with knowledge of the matter.

The shareholder raised its concerns about the Whole Foods' "direction" in meetings with the activist investment funds, Bloomberg reported, without naming the shareholder or the activist shareholders. (http://bloom.bg/2evPBe5)

Several activist investors said they were aware of the shareholder's suggestions and were studying Whole Foods carefully, Bloomberg reported, adding that it was unclear if any activist shareholder had begun building a stake in the company.

Whole Foods shares rose as much as 5 percent to $29.91 in afternoon trading, coming off a halt after the report, before giving up most gains to trade up about 1 percent.

The company had a market capitalization of $9.07 billion as of Thursday's close and its top 10 shareholders include the Vanguard Group, BlackRock Institutional Trust Co and Neuberger Berman LLC, according to Thomson Reuters data.

"Whole Foods Market values the strong and open relationships we have with our shareholders," spokeswoman Brooke Buchanan said in an emailed response.

"We are focused on pursuing the right strategies to position the company to produce strong results and returns for our shareholders over the long term."

Whole Foods on Wednesday said co-founder John Mackey would resume his job as solo chief executive officer six years after he split the role with co-CEO Walter Robb, known as the businessman who carried out Mackey's vision.

The Austin, Texas-based grocer has reported five quarters of falling sales at established stores, and while the decline may be easing, Whole Foods faces intense competition.

(Reporting by Gayathree Ganesan in Bengaluru; Editing by Savio D'Souza)