The 25-year-old Englishman, who led the Hoops' scoring charts in all three of his Parkhead campaigns, moved to Norwich City for an undisclosed fee.
Lennon was naturally disappointed to see his star striker leave but was bullish about the club's future with one European tie successfully negotiated and another one looming on the horizon.
"It's a great challenge and one I look forward to, I'm excited about," he told the official website ahead of the Champions League third qualifying clash with Swedish champions Elfsborg. "No one gave us a prayer when we took the job on.
"We lost Aiden McGeady and Artur Boruc, Robbie Keane had left, as had Marc-Antoine Fortune and Diomansy Kamara, and we had to rebuild the squad.
"It took us a few years to get to where we wanted to be but the core of the squad is still strong. I've still got Brown, Samaras, Forster, Ledley, Forrest, Kayal, Izaguirre, Lustig Matthews...I've got a very good squad and I want to add to that.
"We've brought in van Dijk, Balde and Mouyokolo, who we're pretty pleased with, but we will look to strengthen further and that's the objective now.
"We're trying to push the button on one or two players. We've brought three players in but obviously now a striker, or certainly an attacking area, is a priority for us coming into the next few weeks."
Hooper leaves Celtic with an impressive 82 goals in 149 appearances over three years, and the Lennon was quick to pay tribute to the marksman's time at the club.
"For me he has been one of my best signings in so many ways," he added. "For value for money, improvement, his goals obviously and link-up play.
"I think he's been the best striker here since Henrik (Larsson) and he will be a huge loss to us, but we have to move on.
"He came to me in Germany and he was honest enough to say his ambition was to play in England and he would like the opportunity to take. He has aspirations to play for England, aspirations to play in the Premier League and he's got that now. I wish him well."