By Tony Jimenez

TROON, Scotland (Reuters) - Former Ryder Cup player Francesco Molinari has joined a growing list of golfing withdrawals from next month's Olympics in Rio de Janeiro.

The world's top four -- Jason Day, Dustin Johnson, Jordan Spieth and Rory McIlroy -- have pulled out due to health worries, three of the quartet citing concerns about the Zika virus in the Americas.

"I have decided to withdraw from the Italian Olympic team due to family reasons," Molinari said on Instagram without elaborating.

"I am very disappointed to miss out on golf's return to the Olympics, however I am confident that Matteo (Manassero) will do a fantastic job in my place."

The sport is back on the Games schedule for the first time since 1904.

Manassero joins Nino Bertasio in the Italian team at the strokeplay competition in Rio.

Molinari played in Europe's victorious Ryder Cup teams in 2010 and 2012.

(Editing by Toby Davis)