A major Tribune ( TRB) shareholder disclosed Thursday that it hired a private equity adviser and raised the possibility that it may sell its stake in the media giant.

The McCormick Tribune Foundation, which owns a 11.7% stake in Tribune, said in a regulatory filing with the Securities and Exchange Commission that it hired Blackstone Group as its financial adviser in light of Tribune's ongoing strategic assessment.

The foundation said it signed an agreement to obtain confidential Tribune information and conduct an evaluation of its position in the company, which owns the Chicago Tribune and Los Angeles Times, along with 23 television stations, the Chicago Cubs baseball franchise and slew of other media properties.

The foundation also said it reserves the right to make additional purchases of Tribune stock or dispose of its shares.

Tribune began evaluating strategic options, including a sale of the company, after its largest shareholder, the Chandler family, publicly called on management to change course amid slumping profits and a slide in Tribune's stock price.

Ed Atorino, analyst with The Benchmark Group, says the McCormick Tribune Foundation's latest move means that it's parting ways with management.

"A vote of no confidence may be too strong a comment, but it's certainly a sign that the foundation is at least impatient with the process," says Atorino. "They have been a big supporter of management, and here they are going a separate route. They're looking out for their own interest instead of standing behind management, because management is really dragging their feet on this."

When Tribune CEO Dennis FitzSimons announced in September that the company's board had voted to explore strategic options, the company said it would resolve the process by the end of the year. The company has since extended its strategic review process through the first quarter of next year.

Blackstone Group, the private equity firm hired by the foundation, has also been named as a potential buyer of Tribune.

"You could see a situation develop where the two big shareholders -- the trust and the Chandlers -- get together with other investors and put more pressure on management," says Atorino. "Suddenly you could have a large group of shareholders basically forcing management to accelerate the process."

Shares of Tribune recently were up 9 cents to $31.09.