Fittipaldi broke his left leg and right ankle during qualifying last week for the World Endurance Championship. He is expected to miss about eight weeks.
De Melo takes over the No. 19 car for Dale Coyne Racing. He has competed in three of the first four races this season, all on road courses. His best finish was 17th at the season opener in St. Petersburg, Florida. He finished second last season on Indy's 2.439-mile, 14-turn road course in an Indy Lights car.
Coyne's team has not yet selected a replacement for the May 27 Indianapolis 500 or the June 9 race at Texas.
In announcing Kelly Clarkson as the national anthem singer for the Indy 500, Indianapolis Motor Speedway also revealed that two-time gold-medal Olympian Lilly King would drive the pace car for the IndyCar Grand Prix.
Practice for the IndyCar Grand Prix begins Friday.
The Associated Press contributed to this report.