The former Birmingham City midfielder played under Knill, now the League One club’s assistant manager, during a previous spell with Scunthorpe.
And, after resurrecting his partnership with the 51-year-old at Bramall Lane, Duffy explained how Knill’s advice helped him become a much more effective player.
“Alan was brilliant for me,” Duffy told The Star. “He really worked on my game and improved me no end.
“Looking back then, I was an out-and-out winger. If people couldn’t get the ball to me, then I was pretty much a spectator during matches.
“But he taught me a lot, including how to come inside and be more of an influence. How to dictate things better and drift around. That was much more down to Alan than it was me.”
Duffy, aged 30, signed a pre-contract agreement with United on Wednesday after learning his contract at St Andrews was not being renewed. Previously of Southport, Morecambe and Doncaster Rovers, Duffy was named in the PFA’s divisional team of the year after helping Burton Albion reach the Championship last term.
“Attitude takes you a long way in this game,” Duffy, who spent 10 months on loan at the Pirelli Stadium, said. “And that’s one of the things which really impressed me speaking to the gaffer (Chris Wilder) here. He understands and his really big on that.
“Burton were one of the favourites to go down but they believed in themselves and they believed in their manager. They way we got set-up, we were never going to take a hiding. If we got beat, then we’d get reminded what we were, a good, close-knit group, and not to lose sight of that. Of course, ability was important. But lots of other teams had that. It was spirit and togetherness which probably got us promoted.”
Wilder emphasised the importance of “attitude” and “character” after being unveiled as Nigel Adkins’ successor three weeks ago. Together with fellow new arrival Chris Hussey, Wilder also cited Duffy’s “understanding” of the challenges third tier competition presents as a factor behind his arrival in South Yorkshire.
“The games come thick and fast,” Duffy said. “And so you’ve got to be mentally as well as physically prepared. You’ve got to dedicate your life to it. If you’ve got everyone on the same wavelength, then you can’t go far wrong.”