The 21-year-old was publicly criticised by Mourinho back in early April for failing to produce the required work rate to breach the first team.
He was then handed a chance to mount a resurgence and impressed against Everton, Sunderland and Anderlecht before seeing his season cut short with an injury against Swansea City.
But Irwin, speaking earlier this week, has insisted that Shaw will pick up from where he left off once he makes a return from injury.
“He’s had one really bad injury. No injury is a good injury but (the double leg break in September 2015) kept him out for quite a while.
“Obviously missing pre-season (is not ideal) – as a player, I know how important pre-season is – but we’ve seen what potential he had when he played for Manchester United and coming from Southampton as well.
“I am sure, hopefully, he will come back stronger and be able to compete for that left-back spot.
“I mean, listen, he is only a young lad. He was 22 on Wednesday.
“He is still learning the game – he’ll always learn the game, but particularly when you’re young. Hopefully he’ll get better and better.”
Something has changed – or perhaps emerged – in Shaw’s head. The youngster looked destined for the exit door, unable to summon the chutzpah needed to breach Mourinho’s starting XI.
And perhaps that is exactly what he needed: the prospect of losing out on something he has worked tirelessly towards, threatened once already by a galling leg injury back in 2015.
Mourinho will now give Shaw a second chance after witnessing a strong element of professionalism and drive enter his game, and supporters, especially after seeing the left-back slot change with dangerous alacrity last season, will be desperate to see the Englishman make the most of it.