The 32-year-old has been out of action since being replaced at half-time of the 2-1 defeat to Celtic at the end of February with a knee injury.
Naismith, currently on loan from Norwich City, has missed the last eight fixtures, and is touch and go to be back for the season finale against the Parkhead side at Hampden Park.
He underwent surgery on his knee meaning Levein is already preparing to face Neil Lennon's men without his talisman.
Despite missing 18 games through injury and suspension in total this campaign, the Scotland international remains the club's top scorer with 14 goals.
The forward's deal with the Canaries expires at the end of the season with Hearts desperate to hold onto him with talks already having taken place with the player.
Levein said: "It will be touch and go whether he makes the cup final or not. We've still got a bit of time.
"But the most important thing for me is that we can get Steven signed up on a long-term contract and I want him to be in good health when we start next season. That becomes a priority.
"I'm sure if Steven is capable of playing in the cup final then he will and you know what type of character he is. If he can make it then fine, but I'm not relying on it and we're prepared to play without him. If he makes it then it's a bonus.
"I wouldn't gamble on his fitness. There are things you can risk but then make worse, a lot worse. Certain injuries you can do (take a gamble) with - this isn't that type of injury so the chances of us taking a risk are pretty low.
He added: "We're still working on a new contract for him. We've made another step forward this week and have another meeting set for next week."
Levein was also quizzed about the future of John Souttar who has been linked with a move to Rangers.
The Hearts boss was blunt in his assertion: "I'm not sure John would want to go there to be honest."