Doctors are pleased at the pace Tony Stewart's broken back is healing and have given the three-time NASCAR champion a rehabilitation program aimed to get him back in a race car.

Stewart was injured Jan. 31 in an all-terrain vehicle accident. He suffered a burst fracture of the L1 vertebra and has missed the start of the season, his last as a NASCAR driver.

Stewart-Haas Racing said Wednesday there is no timetable for Stewart's return. Ty Dillon will drive the No. 14 Chevrolet this weekend at Phoenix.