The Swede was the obvious go-to guy last season when the teams were drawn together, having represented both clubs with distinction, and he diplomatically chose not to lend his support to one over the other ahead of the ties. The Swede's neutral position did not stop him revelling in Celtic's 2-1 win at Parkhead, believing it to be the greatest home result in the club's history.
Now Neil Lennon, Larsson's former team-mate, has taken Celtic back into the group stages where another sizeable challenge awaits. If anything the task is harder this time around with Ajax and Milan also lying in wait. Larsson, though, believes reaching the knockout phase again is not beyond Celtic.
"It was fantastic to watch [Celtic] do so well last season," he said. "Now they are in the group stages again and it's absolutely fantastic. Last season's success will help them but they have lost a few players who were important. Is it more difficult this season? Last season's group was difficult and so is this one. Being realistic, you can see that is a very tough group for Celtic. But nothing is impossible. The teams coming to Celtic Park are not going to enjoy it that much. It depends what they can get out of the games here and hopefully do something away from home - then you just never know. There was a wee smile when I saw Barcelona come out of the draw again, as they are two clubs who have been special to me in my career."
Larsson was back in Glasgow to take part in Stiliyan Petrov's charity match at Celtic Park on Sunday. Petrov, another former team-mate, is recovering from acute leukemia and the game between two teams of players, former players, celebrities and other friends raised a six-figure sum for a number of good causes. "It was a great occasion," he added. "Stan was a big part of the group of players we had. We were very tight and still are. It was nice to see so many people turning out to sell-out the stadium and give him a fitting tribute. It was for a good cause and I was honoured to be here. The game wasn't the most important thing, it was about being here for Stan.
"It's always fun to see the guys. We are close and we stay in touch with each other. We had a very special group and even though we are getting a little bit older, you could see that. I think things like this brings you closer together. When something bad happens to anybody that is close to you and you shared so much with, it makes you tighter. It makes you realise that you are not immortal.
"Stan was fitter than most people so you see that it can happen to anyone. It brings you closer together. I met a few of the boys on Saturday when I arrived and it was great. It was fantastic to see that Stiliyan is getting better and better, and that is the most important thing."
Peter Lawwell, the Celtic chief executive, paid tribute to all those who contributed to "a wonderful day" and highlighted Carlos Cuellar, the former Rangers player, as someone who put old rivalries to one side for a worthy cause. Cuellar, now at Sunderland, is said to have spent £11,000 at a charity dinner on Saturday night.
"Sunday was a wonderful day and, first and foremost, it was another chance for the Celtic supporters to show Stiliyan just what they think about him," Lawwell told the Celtic website. "His ability as a footballer always marked him down as a fans' favourite, but the courage he has shown over the past year has been an inspiration, and it was great to see him back out on the Celtic Park pitch again.
"We do pride ourselves on being more than a football club and that was evident again on Sunday. And it was also in keeping with the roots of our club that charity was the real winner on the day. It was great to see so many of our legends back at Celtic Park playing in the Hoops again, and the day wouldn't have been complete without a Henrik Larsson goal. I know that they, along with every other player, didn't have to think twice about agreeing to take part, and that includes a number of Stiliyan's friends and team-mates who are still playing in the English Premier League.
"And I would like to thank them, and their respective clubs, for having agreed to take part. That includes Carlos Cuellar, who not only was eager to take part in the game, but his generosity at the charity dinner the previous night was truly admirable."