News emerged in midweek that the 19-year-old – one of the best prospects to have emerged from the Owls academy in recent years – had signed a pre-contract agreement to join Scottish side Celtic in the summer, when his current Hillsborough deal expires.
It was a move greeted with dismay by Owls supporters, losing one of their best young players.
And their mood would not have improved as Shaw was sent off to swing a crunch relegation battle in the favour of Birmingham City at Hillsborough.
With the game locked at 0-0, Shaw was handed his second yellow card for a needless tackle on 50 minutes, and 14 minutes later the visitors broke the stalemate with a Scott Hogan strike.
Defeat leaves Wednesday next-to-bottom in the Championship and their survival hopes suffering a severe setback.
The Owls made three changes from the side which lost at Stoke City in midweek, Liam Palmer, Matt Penney and Josh Windass coming into the team, Adam Reach, Jordan Rhodes and Osaze Urgohide dropping to the bench.
Having won their previous five outings at Hillsborough, Wednesday came out looking to extend their impressive record.
But with both sides deep in relegation trouble, the opening exchanges were predictable, as both sides treated the ball like a hot potato, kicking long, to avoid making a mistake.
Yet Wednesday should have been ahead after 20 minutes. First Tom Lees – unmarked in front of goal - fired straight at goalkeeper Neil Etheridge, after good work from Callum Paterson.
Then youngster Shaw volleyed over from close range.
The hosts’ third chance of the game was less clear-cut, Barry Bannan – the creative force in the Owls midfield – finding himself at the back post, but his header lacked conviction and was comfortable for Etheridge.
At the other end, City should have opened the scoring, but Gary Gardner headed wide from a free-kick, with the goal at his mercy.
Wednesday were forced to play the final 40 minutes with 10 men, after Shaw picked up his second yellow card.
If his first was harsh – a tackle on Ivan Sanchez - he could have few complaints with his second booking, a lunging tackle and Maxime Colin.
It was the teenager’s second red card this season, after being sent off against Reading earlier in the season.
Shaw’s exit certainly opened the game up, with chances at both ends.
Penney’s cross was only cleared as far as Bannan, but the Owls captain blazed over.
At the other end, Westwood denied Jeremie Bela with a smart save at his near post.
But the Owls goalkeeper was left exposed on 64 minutes as Scott Hogan nipped in to connect with Bela’s fierce drive, and break the deadlock.
Caretaker manager Neil Thompson reacted with a flurry of substitutions, switching to three at the back.
And the Owls came close to snatching a late equaliser, but Etheridge produced a stunning save to deny Jordan Rhodes, whose header looked set for the bottom corner.