One misplaced pass and he was all over you.
As Riley prepared to face a Celtic team built by Lennon, he remembered the standards he demanded as a player and that saw his team claim the championship last season.
Riley said: "Lennon was always fiercely competitive. Every day you had to be on your toes. Personally, I was on the wrong end of a few ear-bashings from him during my time at Celtic. Giving the ball away was his pet hate. If you did that then he'd have something to say about it for sure.
"He expects and demands a lot from those around him and that hasn't changed one bit since he got into management. Everything started in training and if he felt the standards were dropping then he didn't hang about to say so and he didn't care who got it.
"He was a good player though and rarely gave the ball away. He never hid and we've got to be exactly like that. Parkhead is a massive stadium and we can't afford to go there and hide or else we'll get found out.
"Anyone can make a mistake but you can't really shy away from taking responsibility in these sort of games. We've got to go there and keep the ball as much as possible and take whatever chances come our way."
Dundee went back to the bottom of the table with a 2-1 home defeat by Motherwell, but an earlier win over Hearts at Tynecastle gives Riley hope that they can get something in Glasgow.
He said: "Nobody expected us to win [at Tynecastle] but we did it and that should give us confidence. There's no reason why we can't get something from the game against Celtic if we play like we can. It's a stadium that everyone is looking forward to playing at. That's the great thing about being back in the SPL, having such big fixtures to look forward to.
"It's not going to be easy but St Johnstone beat them last weekend, which nobody was expecting either. Hibs got a point at Celtic earlier this season.
"We're starting to find our feet. Last Saturday, once we scored I thought we were pretty much on top and I didn't see Motherwell scoring until that late collapse. We got punished with two late goals which is what happens in the SPL. We've got to learn to cut that sort of thing out but we can still take a lot of positives from the performance last weekend. It's just a fine line between winning and losing at this level which we have to be very wary about."
Barry Smith, the Dundee manager, has promised not to send his team out to cover up at Celtic Park.
He said: "It wouldn't be wise for us to go there and try to defend. That's not in our game-plan so I'll be asking the players to go out and attack as much as possible."
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