Middlesbrough's two Socceroos, McGree and Sammy Silvera, were shattered after all the drama surrounding the Championship playoffs ended with a deflating, last-gasp 1-0 loss.
Key attacker McGree was forced off in the 76th minute of Saturday's final after pulling up from a challenge with a left hamstring issue - just three weeks out from Australia's opening group stage match against Turkey.
McGree was distraught and put his face into his hands before coming off.
He and unused substitute Silvera watched on powerless from the bench as Middlesbrough controlled possession but couldn't find the cutting edge they needed.
Boro received a second chance to go for glory after being reinstated into the final following the expulsion of Southampton, who had beaten them 2-1 on aggregate over two legs in the semi-final but were found guilty of spying on a Boro training session before the tie.
Hull's hero Oli McBurnie scored in the 95th minute to deliver victory for the Tigers.
Socceroos coach Tony Popovic will hope McGree, who likely would have headed in to camp in Sarasota already if not for Boro's late reprieve and will now go for scans, has avoided serious injury.
McGree, an inverted winger in Popovic's system, is one of Australia's most creative and explosive attackers.
But the South Australian, 27, has frequently dealt with injury setbacks, including multiple at Boro this season, and a strain would at least put him in doubt for warm-up friendlies against Mexico on May 31 AEST and Switzerland on June 7 AEST.
Australia's World Cup campaign kicks off against Turkey in Vancouver on June 14 AEST, before games against the United States (June 20 AEST) and Paraguay (June 26 AEST).
The Socceroos copped another blow on Sunday with striker Nicholas D'Agostino withdrawing from camp after suffering a leg injury in training.
It leaves Mohamed Toure, Mitch Duke, Brandon Borrello and uncapped Ante Suto as the No.9s available to Popovic, unless he calls up an alternative, with the 26-player squad due to be submitted to FIFA by June 1.
The celebrations are in full flow for Hull, who are into the top-flight for the first time in nine years, joining automatically promoted champions Coventry and Ipswich in the EPL.
"We felt we'd have one chance and I felt like it was written for me to get it," McBurnie told Sky Sports.
"I didn't think it would be so late on, but what a feeling!"
For Middlesbrough, it was the end of what coach Kim Hellberg called the "toughest two weeks I have had in terms of emotions".
"Tough and draining, but it is not an excuse -- we were ready to play the game, Hull scored the goal and we have to congratulate them."
The match was once again hailed as the football world's most lucrative one-off contest, because a windfall of at least $A380 million in future earnings was at stake for the winners.
Boro's Wembley curse continued as they have now lost for the sixth time in as many appearances, leaving plenty of frustration for McGree, in particular, who's had playoff heartbreak before with Boro, having lost out to Coventry in the semi-finals in 2023.
Hull's Bosnian manager Sergej Jakirovic, whose side only sneaked into the play-offs in sixth place on the final day of the regular season, said: "A lot of players were crying with happiness at the final whistle".
"It's incredible. An unbelievable journey -- so many problems, so to achieve the Premier League is incredible."
With agencies
