Blackstone Group and Advent buyout funds are in the hunt to buy a majority stake in Kantar, WPP's big data analytics firm, according to a report in Reuters.
WPP's board in October announced plans to seek a strategic or financial partner for Kantar.
CFO Paul Richardson in November said WPP was willing to part with an 80 percent stake in Kantar, as part of its overall turnaround plan.
CEO Mark Read in December said WPP received "numerous unsolicited expression of interest" in Kantar. He said a second-quarter announcement of a deal was likely.
Goldman Sachs, which is shopping Kantar, said the sale would value the research output in the $4.7B range.
Reuters said Bain Capital, Hellman & Friedman and CVC Capital Partners may also get involved in the Kantar bidding.
WPP sent out information pacts this week and anticipates a round of non-binding offers in April.