Lennon played with Modric at Tottenham during the Croatia midfielder's four years in north London where his Premier League form earned him a move to Real Madrid in 2012.
In Spain, he has cemented his place as the best in the game, winning three league titles, five Champions Leagues, two domestic cups and five Club World Cups.
Modric has played more than 500 times for Real and won the Ballon d'Or in 2018 after helping Croatia reach the World Cup final.
"Honestly, some of the things I've seen him do in games - just running games from the start to the finish. He was just a genius," Lennon told talkSPORT Drive when asked who the best player he played with was.
And Lennon has played with some of football's best players, including Gareth Bale, who joined Modric in Spain a year later and England's so-called 'Golden Generation' that included David Beckham and Steven Gerrard.
He was part of the 2006 World Cup squad that reached the quarter-final in Germany, replacing an injured Beckham against Portugal.
On Modric he added: "When he first came we saw glimpses of it and we were thinking, 'oh this guy is special' but then it wasn't until certain games against the big boys when it was like, wow, he can literally put us on the same level as them and run this game.
"The only other player who I've seen run a game like that was Steven Gerrard. They were the two who could completely control the tempo of a game, but Luka was a genius of a footballer.
"You couldn't get [the ball] off him and he was my size! Playing in the middle of the park, no upper body, but big legs to be fair to him!"
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Asked if he thought he would go on to be the best player in the world, Lennon said: "I'm not sure about that, but it didn't surprise me because he was improving year by year and then once he left Spurs he just rocketed."
Modric earned 753 points to win the Ballon d'Or compared to second place Cristiano Ronaldo on 478, with Antoine Griezmann in third followed by Kylian Mbappe and Lionel Messi.
At 38 years old, his time as Real Madrid's main man is nearing it's end but his influence is still felt, with Jude Bellingham learning from the maestro.