Celtic sent shockwaves across Europe with their Champions League success 9 years ago and Sir Alex Ferguson had a role in the Hoops' success.
Speaking back in 2012, then-manager Neil Lennon said: "Sir Alex gave us two hours of his time and it was a brilliant gesture. It was in the privacy of a room at the training ground, just myself and my backroom staff, some tea and pancakes.
"He was in great form. He has given us little titbits along the way. I'm not saying that has got us over the line but every little bit helps. He was one of the only managers to write me a letter when we won the league in May and I'll be eternally grateful."
Celtic beat Benfica and Spartak Moscow to the second-place finish in the group stages in 2012, securing a historic 2-1 win against Barcelona at home in the process.
Lennon saw his side's Champions League adventure come to an end in the Round of 16 where they were beaten 5-0 on aggregate by Juventus.
