“I feel really awful,” said the actor, who has charity work commitments.
Leonard Nimoy and William Shatner, pictured on Aug. 19, 2006.
Ethan Miller / Getty Images
"I loved him like a brother. We will all miss his humor, his talent, and his capacity to love," Shatner said on Twitter.
Nimoy, famous for playing the Vulcan Mr. Spock, died Friday from end-stage chronic obstructive pulmonary disease at the age of 83.
"I am so humbled by the worldwide outpouring of love that has been displayed; words cannot express my feelings," Shatner wrote.