Forster, who has been named in the England squad for next week's friendly against Sweden, has been dubbed 'La Gran Muralla' - The Great Wall - by Spanish media after producing a string of brilliant saves in the Champions League clash.
Lennon said: "Joe Hart is a wonderful goalkeeper and arguably one of the best in the world but this kid is coming. He is only 24 and is getting better each passing season.
"He works ever so hard behind the scenes. He is 6ft 6in and is very agile. He fills the goal and is fantastic at taking crosses.
"When you are in Europe playing against the cream you need your goalkeeper to be big and he has a fantastic temperament. In the two games against Barcelona he has excelled and he is a huge reason why we are where we are in Europe."
Lennon has also warned his team not to take qualification for the knockout stage for granted following the win.
"It doesn't stop now," he said. "That's four games in a six-game campaign at this level. Just because we beat Barcelona it has not guaranteed us anything yet.
"Our aim was to qualify. We are taking it game by game and not looking at the permutations of what happens elsewhere.
"We are going to try and go to Benfica and get a positive result and if we can do that it will give us a magnificent chance."