10 Changes Star Trek Hoped You Wouldn't Notice
7. Doctor Pavel Chekov
Star Trek Generations was both the first cinematic outing for the Next Generation crew and the final one for several of the Original Series actors. The script was always going to feature William Shatner returning as Captain Kirk, which would end up with Kirk and Picard coming face to face. Two other faces from the earlier Enterprise were to join him, at least for a while - Spock and Doctor McCoy.
Leonard Nimoy was approached about returning, as was DeForest Kelley. The former refused after he discovered that Spock's role would only be a cameo. He had no interest in appearing or directing, in a film that treated Spock as a throwaway character. Kelley on the other hand was unable to secure insurance to return, due to his ailing health.
This left the writers with a script written for Spock and McCoy, with no chance of the actors returning. In a clumsy move, Scotty and Chekov were slotted into their places. Scotty's dialogue is slightly more stilted than it would normally have been, as he was given Spock's lines almost wholesale. Chekov, for his part, seems to have switched departments from Ops and Security to Medical. He takes over in sickbay, recruiting two reporters as nurses on the way. While it is a good scene for the character, there had never even been a mention of his Medical training before.
The truth is that the entirety of shots featuring Scotty and Chekov were simply (and poorly) veiled attempts to hide the fact the other two actors weren't returning for the film.