The 19-year-old agreed a four-year deal with Celtic on Friday morning, seven days after he had initially rejected what the club described as a “magnificent” contract offer.
Turnbull subsequently travelled south for talks with Norwich City and appeared set to join the English Premier League newcomers, prompting an angry reaction among many Celtic fans.
But in a dramatic turnaround, the attacking midfielder re-opened talks with Celtic late on Thursday night before arriving at Parkhead the following morning to shake hands on a deal with Lennon.
The Celtic manager says he is unaware whether improved financial terms were offered to Turnbull but insists the club’s support should welcome the player’s eventual decision to choose them ahead of a move to the English top flight.
“I wouldn’t have thought there would be a problem with the fans,” said Lennon. “Once the fans are aware David has chosen Celtic over a Premier League club, they will be very impressed with that.
“Listen, you’ve got to take it from David’s point of view as well as his representative’s point of view. They’ve got to look at all of the options available before they come to conclusions.
“I know we’re a big club and a big draw. But there are other mitigating circumstances that maybe we don’t know about, that might’ve prolonged the signing.
“Yes, I was surprised when it was back on again. I was under the impression he might’ve wanted to go elsewhere. But then he’s obviously had a serious think about it and decided he wants to come to us.
“I spoke to him on two or three occasions after the fee had initially been agreed with Motherwell and, again, it was all very positive. But David had to take advice from his advisors, that’s what they are there for.
“There were a few twists and turns in this one. But in the end I think the player himself decided we were the best option for him, which we agreed with obviously.
“Obviously, he’s spoken to his representatives and they’ve come to the same conclusion. From what I gather he was down at Norwich, having a look around and was impressed. But he felt that Celtic was the best place for him.
“To choose us over a Premier League club is quite a statement from our point of view. We’ve been tracking him for a while. He’s a fantastically gifted young Scottish player, so we want to try and get the best out of him in the coming years.”
Turnbull scored 15 goals in a stunning breakthrough season at Motherwell which saw him named as Scotland’s Young Player of the Year.
Lennon is confident he can hold down a regular first-team place at Celtic and provide qualities in the attacking third of the pitch the manager felt his team lacked last season.
“That’s exactly what is good about David,” added Lennon. “It was a big big plus in his favour as far as I was concerned. We need more goals from midfield and hopefully David will provide them.
“He’s a Stuart Armstrong type. I felt we were lacking that a bit. I thought last season we played a lot in front of teams and David will go beyond. I also think he’s a good finisher once he gets into position. Technically, he’s proficient with both feet and manipulates the ball very well.
“It’s always the sign of a good player that he constantly appears to have time and space on the ball. Amid the hurly burly, they appear to slow the game down, but they don’t really. It’s just his composure.
“His stats are excellent. For someone so young, to explode onto the scene that way was impressive. He was too good a talent for us to ignore.
“He’s quick, an impressive character in the way he plays and also in the way he handles himself off the field. There’s a maturity about him for someone of such a young age.
“We’ve got a proven track record in developing players and I think that works in our favour. We’re hoping he’ll join the ranks of James Forrest, Callum McGregor, Kieran Tierney plus the likes of Victor Wanyama and Virgil van Dijk. The type of players who have a great career here and also have a pathway of maybe progressing their careers even further later on.”