The mystery benefactor stepped in to pay for a an £18 turkey crown at the shop in Firth Park after the woman in front of him admitted the price was too high for her to afford.
And customers at Patterson's in Bellhouse Road have praised the man for his good after the shop's Facebook post describing the incident was shared hundreds of times.
Posting earlier this week, the shop wrote: "We didn’t get your name.
"What a great guy... an old lady asked us to weigh her a turkey crown. £18 was the price - unfortunately the lady couldn’t stretch to that amount. She got her shopping and left.
"The guy directly behind asked for the same crown. He then paid for it and asked us to wait. He ran down the street and gave it to her.
"We might get some bad press in Firth Park but this guy proves what lovely decent people there is here. You're a top top man. Merry Christmas to you and yours. Amazing gesture."
The move was praised by customers who congratulated him on his festive spirit.
Michael Stead wrote: "Proves there is still some good people out there."
Philippa Sykes added: "What a wonderful thing to do, a big high 5 to the gent."
David Smith posted: "Well done that man. Good manners and heart" while Kerry Bowers added: "Aww how lovely . What a sweet guy."
Nina Marie wrote: "Nice 1 that's what Christmas is all about."
Gail Lymer added: "Well done fella!! But he didn’t do it to get the glory he just wanted to help the old lady, I would imagine that's reward enough for him! Merry Christmas whoever you are!!"
Jill Matthews added: "What a lovely, kind thing to do, people around here get a bad name but most are lovely, I hope that karma is kind to him and his family in return."