Ljubicic won bronze in the men's doubles at the Athens Games in 2004
Croatia have suffered a double blow ahead of the Olympic tennis event with the withdrawal of both Ivan Ljubicic and Ivo Karlovic.
Ljubicic, a former world number three who has slipped to 51 in the rankings, pulled out with an unspecified injury.
His place has been taken by Devon Mullings of the Bahamas, the world 1025, who now plays Argentina's Agustin Calleri in the first round.
Karlovic withdrew on Friday after developing a high temperature.
His place was taken by Chinese youngster Yu Xin Yuan, who gets his tournament underway against Tomas Berdych of the Czech Republic.
Karlovic, the world number 18, recently defeated Roger Federer in Cincinnati.
Croatia had already lost Mario Ancic, who pulled out earlier this month because of illness, and have Marin Cilic as their only men's hope.
The tennis tournament begins on Sunday 10 August.