Lennon said, "I spoke to the referee about his performance and he then showed me a red card while I was shaking hands with the Rangers players.
"Clearly, although I felt the red card - my first in the SPL - was totally unjustified, I understand that my reaction was wrong.
"I apologise for my reaction towards the referee and his assistant and I also apologise to Celtic and our supporters."
Lennon will now face a hefty suspension - possibly up to eight games.