The Denmark-based midfielder, who failed to make the Confederations Cup cut, had that sinking feeling again - until he got a text from Socceroos management on Tuesday informing him he'd been handed a reprieve.
Skipper Mile Jedinak's pain was Amini's gain, and a plane ticket to Saitama was punched for the one-cap AFG Aarhus midfielder after the Aston Villa talisman failed at the eleventh hour to prove his fitness after a long recovery from groin surgery.
The 24-year-old knows that translating his call-up into a second cap against the Blue Samurai is a long shot.
Nonetheless, he's elated to have the chance to enter coach Ange Postecoglou's orbit once again.
"I've played the last five games for my club, seeing out 90 minutes, so initially it wasn't a good feeling (not to be selected in the final 23 for Japan)," said Amini.
"But when you get called in you get called in, and you are happy about it of course.
"The message came through (on Tuesday) and I was really pleased.
"Injuries (to players) is part of football, it happens all the time and now I just want to come in and hopefully we will do the job against Japan."
Having collected two man-of-the-match awards for his club this season, plus a brace of team-of-the-week selections from his six starts, Amini will head into camp on Sunday in a bouyant mood.
He has always persevered in the face of a seemingly endless uphill struggle to crack a regular place on the Socceroos inner sanctum.
"I'm a positive person and I believe that if you work hard the chance will come," he said.
"I've done quite well so far in the early part of the season.
"I'm an important player in my team and that means a lot to me."
Amini even wore the captain's armband at the weekend after AFG skipper Martin Spelmann was replaced in the 2-0 win over Brondby.
His Socceroos debut against the UAE in March encompassed just four minutes off the bench, and has whetted the appetite for more.
"I'm looking forward to going again and getting another taste," he declared.
"The national team have a great set-up and there will be no excuses.
"You go there, you work hard and if the chance comes I will be ready, that's for sure.
"I want to be able to contribute more but that's of course up to Ange."
Amini believes Postecoglou's high energy, pressing style, which cherishes possession over pragmatism, suits his game.
"The way Ange wants to play suits me," he said.
"He wants to hold the ball and move the opposition around.
"I've enjoyed being around him, his team talks and the whole intensity surrounding everything he does.
"I'll be working extra hard and doing everything I can to get that chance to play."
Amini knows, however, that competing for game time with the likes of Aaron Mooy, Massimo Luongo, Jackson Irvine and Mark Milligan will be daunting.
"We have a strong midfield, just look to how Aaron Mooy is going in the Premier League at the moment," he added.
"I am just proud to be involved, I've been over here in Europe battling it out since I was 18.
"I have never given up and it's been paying off.
"The Japan game is absolutely massive. It's almost a final but if we are on our game we can beat anyone.
"Out mental strength is strong and we will battle till the end."
Australia need at least a point against Japan, and then three in their final Group B game against Thailand in Melbourne five days later to seal automatic qualification for Russia 2018.
It could be a reunion in Saitama for Amini and former Borussia Dortmund teammate Shinji Kagawa.
Though they never played together in the first team, Amini struck up a rapport with his fellow midfielder during training sessions.
"I'm looking forward to seeing him again, he said.
"We were always mucking around at stuff and it will be nice to see him after a long time."