Shatner, 83, took to twitter to express his disappointment for not being able to attend the funeral today, reported Ace Showbiz.
"I am currently in FL as I agreed to appear at the Red Cross Ball tonight. Leonard's funeral is tomorrow. I can't make it back in time," the actor tweeted.
"I feel really awful. Here I am doing charity work and one of my dearest friends is being buried," Shatner continued.
Nimoy died at the age of 83 Friday morning, February 27 at his home in Los Angeles after battling chronic obstructive pulmonary disease due to his long history of smoking.
His passing came a few days after he was hospitalised at UCLA Medical Center for severe chest pains.