Shares are 1% lower after hours, following a 1.4% gain today.
Nielsen will push back the deadline for last bids until June and has cut its asking price to keep Advent and Goldman Sachs interested in the deal, according to the report.
That would explain the lack of developments after final bids were thought to be due in April.
Advent is reportedly working a creative structure to make a bid for the company, which has an $8.5B market cap along with $9B in net debt.
Subscribe for full text news in your inbox