The 20-year-old, who is on loan at Ipswich Town, had first-hand experience of the former Republic of Ireland international during a training session as he rose through the ranks at Old Trafford.
Speaking to the East Anglian Daily Times, Tunnicliffe said: "I've taken squad number 16 because Roy Keane was my idol growing up. He was a hard tackling midfielder which is what I like to be.
"When I was a bit younger he was doing his coaching badges and I had one session with him. I'm a Manchester United fan, I had a season ticket and I used to watch him thinking 'I want to play like that'.
"He was a winner, he was 110% in everything he did, not just in games on a Saturday but in training as well. That was his character and I picked up on a lot of that. Sometimes you might not be the best footballer in the world, but if you want to win – and want to win badly – that beats someone who is more talented, but doesn't have that same desire."
Tunnicliffe is expected to make his Ipswich debut away at Reading this afternoon.