Activist investor Elliott Management Corp. said on Monday it would push Nielsen Holdings to look into a sale of the TV-ratings company including options where Elliott would be a potential buyer of, or investor in, its businesses.

Elliott said in regulatory disclosure that it now had a 5.1 percent stake in Nielsen, whose shares (NLSN.N) have fallen nearly 40 percent this year but were up 15 percent at $25.65 in trading before the bell on Monday.

Elliott now holds the fourth biggest stake in the company, after Vanguard Group, Fidelity Management and Capital Research Global investors, according to Thomson Reuters data.

The disclosure also showed Elliott had an economic interest of about 8.4 percent of Nielsen's outstanding common shares, including derivatives and stock options.

Nielsen said in a statement emailed to Reuters that the board and management regularly engaged with shareholders and welcomed the views and perspectives of its owners, including Elliott.

The company said last month it was conducting an in-depth strategic review of its business.

Nielsen, which is known for its television ratings that are used to determine ad rates for traditional TV commercials, has missed Wall Street estimates for profit in seven out of the last eight quarters.

The disclosure confirmed an earlier Wall Street Journal report that said the activist investor held a position in Nielsen and was pushing for a sale of the company.