Penske Racing has not named a replacement for this Sunday's UAW-GM Quality 500 at Lowe's Motor Speedway in North Carolina.
The 32-year-old Mayfield has been having a disappointing year with just five top-five finishes in 30 races. His best results were three third-place finishes at Rockingham, North Carolina, Bristol Motor Speedway in Tennessee and Watkins Glen, New York in August.
Since then he has not finished better than 13th in six races and is a lowly 22nd in the points standings. Mayfield has also been struggling in qualifying, making the grid 30th or lower in 12 events.
Penske Racing also fields cars for veteran Rusty Wallace and Ryan Newman.
Mayfield had been with the team since 1996 under the ownership of Michael Kranefuss. Roger Penske became a part-owner in 1998.Mayfield has three Winston Cup victories, two of which came at Pocono Raceway in Pennsylvania.