Everton were beaten 1-0 by West Bromwich Albion yesterday.
Lennon was substituted off in the 74th minute of the contest and replaced by Gerard Deulofeu.
The change was greeted by widespread jeers at Goodison Park, but Martinez insists that he did not make the switch as a reflection on the former Tottenham Hotspur winger’s performance.
"We've got a good squad in numbers, and Aaron performed really, really well, and just to have a bit of fresh legs when you see a player who is defending for 90 minutes, like the left-back was, and obviously he was booked when you've got a fresh pair of legs,” Martinez explained.
"Deulofeu is someone that in one-on-one situations can create something out of nothing, so it's making sure you use your substitutions and the quality we've got in the squad.
"It wasn't anything about the performance of Aaron Lennon, I think he was outstanding for the time he was on the pitch.”
Lennon had looked like one of Everton’s most potent outlets before his withdrawal yesterday.
The England international created plenty of chances for his teammates, but they were ultimately unable to break West Brom down.
Everton had 34 shots in the match, however goalkeeper Ben Foster proved to be unbeatable as the Baggies picked up a hugely important three points.
The defeat has seen Martinez’s side drop down to 10th in the Premier League table and it is has ended their run of three straight victories.