Mario Ancic of Croatia celebrates winning the second set against Bobby Reynolds of the United States during the BNP Paribas Open on March 11, 2010 in Indian Wells, California.
Former world number seven Mario Ancic has retired at the age of 26 to become a lawyer after years battling illness and injury.
The big-serving Croatian, who earned the nickname "Super Mario" after reaching the Wimbledon semi-finals in 2004, achieved his career-high ranking in 2006 but has struggled since with the illness mononucleosis as well as back and knee problems.
"I can't stand it any more, I have finished my career," Ancic was quoted as saying by Croatian daily Jutarnji List on Monday.
"I'm forced to quit because nature has decided it's time. My back can't withstand the effort of professional tennis."
Ancic, whose greatest moment came in 2005 when he won the deciding rubber in the Davis Cup final against Slovakia, is due to hold a news conference on Wednesday.
During his lengthy spells out of tennis Ancic, whose father owns a supermarket chain in Croatia, studied for a degree in law at the University of Split which he completed in 2008.