WPP Group has opted out of the McDonald's review, Ad Age has learned.

The holding company was invited, along with Publicis Groupe and Omnicom, to participate in the review for the fast-feeder's U.S. creative account, the bulk of which is currently split between Omnicom's DDB and Publicis' Leo Burnett, both in Chicago.

With WPP out now, it appears as though the incumbents are left to compete against one another. WPP's choice to back out of the review may have something to do with finances or the tight turnaround of the process, which is said to be around 60 days, according to people familiar with the matter.

WPP referred calls to the client. McDonald's could not immediately be reached for comment.

The chain launched the review on April 25, in search of a more uniform set of creative and strategic ideas, and the means to push those concepts quickly across the different media it uses. This is the first request for proposals to go out under McDonald's U.S. Chief Marketing Officer Deborah Wahl, who joined the Golden Arches in March of 2014.

Despite the review, McDonald's is expected to keep its longtime tagline "I'm lovin' it." The process will not affect McDonald's host of other agencies, including Omnicom's OMD, its media agency, and sibling Alma, which handles multicultural. Also not affected is its PR agency, Golin Harris.

The review comes as McDonald's works on a turnaround after a protracted sales decline, spearheaded by CEO Steve Easterbrook and U.S. President Mike Andres. Sales began decelerating in early 2012, though the company has seen some sales increases more recently, thanks in part to the rollout of its all-day breakfast platform. McDonald's reversed the two-year decline in U.S. same-store sales in the third quarter of 2015.

McDonald's spent $1.42 billion on U.S. advertising in 2014, making it the 26th largest advertiser in the country, according to the Ad Age Datacenter.