Speaking to United Review, Steele revealed that he went to watch de Gea play 17 times for Atletico, with one particular display in 2010, a full year before the deal was complete, telling him that the Spaniard was the real deal.
"There's always a chance being taken while you're scouting, but I saw David in the Europa League semi-final at Liverpool and that clinched it for me," Steele explained.
"He was phenomenal. He did things in the first 25 minutes of that game that made my mind up. I could have left after half-an-hour with the decision made. You think of the atmosphere, the state of the game… he didn't look an 18-year-old lad."
An extra-time away goal from Diego Forlan ensured that Atletico won that tie en-route to lifting the Europa League trophy, de Gea's first silverware in senior football. His first year in England was a real challenge, though.
Steele, who left Old Trafford in 2013, was a key figure in de Gea's early development at United. The youngster famously struggled at first, but his coach worked tirelessly to help him adapt and fulfil his potential, even starting to learn Spanish to help de Gea feel more at home.
Despite extending the search for a new stopper far and wide, Steele admitted there was never really anyone else seriously in the picture after he'd seen de Gea.
"You look and go: 'Wow. There's maturity, calmness beyond his years,' and that really was the start of me saying to myself that his was a special talent," he continued.
"And that's been proven. He's a very special talent in the goalkeeping world. We looked all around the world for a replacement for Edwin, but we always came back to David.
"Ultimately he was very well scouted and the decision was made by the main man, the manager. Sir Alex [Ferguson] was never afraid to bring young players into the club and blood them in the team. In terms of a goalkeeper, that's what we did for the first time with David."
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