BRUSSELS, Oct 2 (Reuters) - EU antitrust regulators will widen a probe into Zimmer Holdings Inc's $13.4 billion bid for Biomet Inc but clear Eli Lilly's offer for a Novartis AG unit, three people familiar with the matter said on Thursday.

The two deals are among several announced in recent months in the healthcare sector, with drugmakers seeking to gain scale or specialise in certain disease areas.

The European Commission, which has been reviewing the deal since August, will open an in-depth investigation into the Zimmer, Biomet deal because of concerns that it may reduce competition, the people said.

The acquisition would make U.S. medical device maker Zimmer the second-largest seller of orthopaedics products behind Johnson & Johnson, boosting its presence in the fast-growing sports medicine sector.

In contrast, the EU competition authority had no issues with U.S. drugmaker Eli Lilly's proposed $5.4 billion takeover of Swiss peer Novartis' animal health business, the sources said.

(Reporting by Foo Yun Chee; editing by Barbara Lewis)