Former Swansea City manager Martinez recalled how he threw Allen into the fray in a frenetic end-of-season clash with Blackpool, and knew straight away he had a potential top-flight performer on his hands.
Martinez explained: "I know him really well because I gave him his debut at 16, and I had a very intense period with Joe to make sure he developed in the right way.
"It will be great to see him again. When you give someone a league debut it has a special effect. Joe was at Swansea from when he was nine and because of his slight build he always reminded me of Pep Guardiola and those sort of players.
"They had to be masters at what they are doing on the ball because they could not go into 50-50s, could not compete for the ball so well physically, and so he developed that incredible technical ability.
"When Joe played against Blackpool I really tested his character that day. And at the age of 16 he came on and you could see he was special.
"He dictated the play, he wanted the ball, and then the season after he played a part in the campaign when we won League One, and then in the Championship he played 27 games at a young age.
"His development was progressive and he became a very different British player. He was very talented in that he could control the game, read the tempo. He knew when to play backwards and sideways instead of just charging forward. In that respect he was a quite distinctive young player coming through the ranks."