Both spent time at No. 1 in the rankings in 2003, when Roddick beat Ferrero in the U.S. Open final -- the last time an American man won a major singles title
The 11th-ranked Roddick pulled out of the Italian Open doubles final last weekend and the singles event at this week's Open de Nice to give himself a chance of recovering in time for Roland Garros.
The French Open draw is Friday, and play starts Sunday.
Roddick is mired in a four-match losing streak in singles dating to mid-March.
His game is built on a big serve and forehand that are slowed by the red clay of Roland Garros, and in nine trips to the tournament, he's made it as far as the fourth round just once, in 2009. His career French Open record is 9-9, including four first-round losses.
Ferrero has only played five matches this season and is ranked 72nd this week.
In addition to his French Open title, he was the tournament's runner-up in 2002.
Organizers also said that 78th-ranked Richard Berankis of Lithuania pulled out because of a hip injury. All three men who withdrew Thursday will be replaced in the field by a player who lost in qualifying.