Leffler was 35th in the Nextel Cup points standings and did not have a top-10 in 19 starts. His best finish was 12th in the Advance Auto Parts 500 at Martinsville, Va., but he failed to qualify for the Coca Cola 600 and finished 33rd last week at the Brickyard.
"Everyone at Joe Gibbs Racing had high hopes for Jason and the No. 11 team, but our performance wasn't meeting the expectations all of us set forth at the beginning of the year," said JGR President J.D. Gibbs.
For his Nextel Cup career which began in 2001, Leffler made 62 starts with one pole and no wins. He was the pole-sitter at Kansas in 2001.
Terry Labonte will drive the No. 11 FedEx Chevrolet this weekend on the road course at Watkins Glen International in New York.