Leonard Nimoy was concerned about Zachary Quinto taking on the role of Spock in 'Star Trek'.

The 79-year-old actor - who played the pointy-eared first officer in the original TV series of the galactic-based franchise - admits he was happy for Quinto to play Spock in the 2009 movie reboot, but was worried about him knowing what was involved with working on the film.

He said: "They sent me some footage to look at when they were deciding who should do that job. I said, 'He looks enough like me to make it work.' But more importantly you can see him thinking, there's a brain, there's some thought going on, which is very important to this character because there's so much inner life in the Spock character.

"Zachary is a very well-trained and intelligent actor... I'm very flattered to see the character live on with a good actor.... But when we first met, I said, 'Do you have any idea what you're getting into?' "

The American star, who recently announced his retirement from the acting profession, also revealed at the Los Angeles Times Hero Complex Festival that William Shatner was concerned about being directed by Nimoy in 'Star Trek IV: The Voyage Home'.

He said: "When Bill Shatner heard I was going to direct a 'Star Trek' movie he went into deep shock. He was really worried. Look, everybody knows that we have become very, very good friends. But we've always been like two competitive siblings. But as for me directing him it worked out pretty well."