St. Louis Cardinals legend Lou Brock is undergoing treatment for multiple myeloma, a form of blood cancer.
Brock was recently diagnosed with the disease, according to the Cardinals. The club said Brock is undergoing treatment in St. Louis.
The illness led to the 77-year-old Brock cancelling a planned April 25th appearance at Busch Stadium.
"I am disappointed that I won't be able to make the event," Brock said in a statement. "Jackie and I appreciate the prayers and support we have received from our many friends and fans in the Cardinals community.
"We count ourselves blessed that I am receiving the best possible medical treatment and we look forward to seeing many more Cardinals World Series Championships in the future."
Brock was a six-time All-Star during 16 seasons with the Cardinals from 1964-79. The Hall of Famer stole 938 career bases, including 118 in 1974, a record later broken by Oakland's Rickey Henderson.
Brock also battles diabetes and had his left leg amputated below the knee in 2015. He has since been fitted with a prosthetic.
Brock played 19 total major league seasons, the first three with the Chicago Cubs.