Warren, 26, scored Grimsby's second goal as the fourth tier side went 2-0 up against Premier League side United before winning in a dramatic penalty shoot out this week. It was one of the biggest cup upsets in history and will not be forgotten in either club’s history for decades to come.
In a post on Instagram, Warren shared some pictures of his celebrations and wrote: "Kauzzzy Fingyy," followed by a rocket emoji. The post was liked by United loanee Marcus Rashford who is currently at Barcelona after escaping the so called “bomb squad” this summer.
Warren spoke to The Manchester Evening News about their bond from their academy days to now which rubs salt in the wound for United who crashed out of the cup before most Premier League sides enter it.
"There were a few of us at the time, all the same ages, all from Manchester - from the same area in Manchester - playing for the same local teams in that area and district," he said.
"So it was easy to get on with each other and get to know each other.
"He (Rashford)'s been to a few of my games with the rest of my mates - and it's interesting to see he'll still come and watch with his mates. He's not forgotten about friendship and it's all about friendship."
Warren left the club in 2019 after being released, joining Salford City to start his career in the lower leagues which of course eventually led to Grimsby where he sent a message to United in dramatic fashion.