The Hoops midfielder was shown a straight red card for kicking out at Neymar just before the hour-mark of the Scottish giants' eventual 1-0 loss to Barcelona at Celtic Park in the Champions League group stage.
The sending off of Brown changed the game as Barca went on to score the winner in the 76th minute through Cesc Fabregas and it left Lennon with a sour taste in his mouth after a fairly solid performance from Celtic.
"I think it is very soft. I have looked at it," he said after the match.
"If there was any contact, it was minimal. There was a lot more in a game that warranted heavier punishment.
"It was a game-changing decision. It is obviously very difficult playing Barcelona with 11 players and even more difficult with 10 but we played very well tonight.
"I don't think the initial tackle was a severe one. It is a physical game I don't think Neymar does himself any favours with the way he behaves at times.
"Our supporters are very respectful of great players. Iniesta walks off tonight to a standing ovation from the Celtic support. After the incident Neymar gets booed every time he touches the ball."
Lennon added: "There is no question it is a foul, but the reaction didn't merit it.
"The referee was going to book Scott for the initial foul but for the tap, if you want to call it that, he has sent him off. Is it violent play or dangerous play? I am not so sure.
"There was a lot of heavy challenges going on in the game. Was that a sending off? Not in my view."
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