England winger Lennon arrived from Tottenham Hotspur on loan for the rest of the season shortly before the January transfer window closed on Monday.
Martinez believes that the 27-year-old, who struggled to nail down a place in the first team under Tottenham's new manager Mauricio Pochettino, is match-fit and ready to play.
"Aaron is very focussed, ready to train and perform," Martinez told a news conference on Thursday. "When you sign a player in January it is very difficult to find someone who is up to speed with his fitness.
"But he is. He's an incredible player, he is fully fit, and ready to make an impact and be involved at the weekend -- that is very rare with a January signing.
"Will he start the derby? We have to be careful and make sure he knows the way the team plays. But I expect him to be in the squad and he has a massive role to play over the next few weeks, when we have a lot of games."
After an indifferent season, instead of a familiar challenge for the league's top four, Everton are 12th but are unbeaten in their last three league games.
They will be without first choice goalkeeper Tim Howard, who has recovered ahead of schedule from a calf injury but is still a week away from full fitness, for the visit of in-form Liverpool with Joel Robles continuing to deputise for the American.
Martinez says the recent form of both sides guarantees the derby will live up to the fast and frenetic battles of the past.
"The Merseyside derby is one of the most special games in world football," the Spaniard explained.
"The last one (a 3-3 draw at Goodison Park) was a phenomenal football game with plenty of goals, both teams with an attacking mindset. I expect the same on Saturday.
"Liverpool are on a good run and we feel similar in terms of the confidence the win at the weekend gave us (1-0 at Crystal Palace)."
(Reporting By Sam Holden; editing by Sudipto Ganguly)
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