Celtic suffered a late slip-up in the Europa League on Friday morning (AEDT) as Bayer Leverkusen came from behind to claim a late 3-2 win.
In a game they couldn't afford to lose, the Hoops conceded first but found the lead in the 56th minute after Jota found the back of the net.
Ange Postecoglou turned to his bench in the 76th minute as he brought on James McCarthy and Albian Ajeti at the expense of Nir Bitton and Kyogo Furuhashi.
Those substitions wouldn't work as planned, however, as Leverkusen equalised just six minutes later through Robert Andrich before Moussa Diaby scored a stunning volley in the 87th minute to win the match.
The defeat means Celtic now can't escape their group and some believe the player changes cost them the game against Leverkusen.
Celtic subs haven’t worked tonight. Gutsy performance and the truth is the Celtic team have improved so much under Postecoglou. Big shame though. Defensively Celtic have come up well short in Europe. Overall squad strength not as strong as Ange would like. January a key month!
— Chris Sutton (@chris_sutton73) November 25, 2021
Postecoglou made an arse off this with those awful subs
— Oran (@oranstorrie99) November 25, 2021
Thats a sore one. I get the logic behind subbing off front 3 but that killed us going forward. Felt subs couldve been made 5 or 10 minutes later.
— Ronnie Postecoglou (@RonnieJM67) November 25, 2021
As much as I admire the work he has done so far with Celtic, Postecoglou has a share of the blame tonight. Subs changed the game. Kyogo and Jota off 🤔 Only looked like 1 winner after that! Hoops battled tho and played decent. HH
— Cathal Toland (@Caks88) November 25, 2021
The Hoops had been on a nine-match undefeated run and showed significant signs of progress considering they lost 4-0 against Leverkusen in early October.
Postecoglou concedes his side were always battling to stay in the contest but feels they have taken another step forward despite the result.
"It is a tough one. We kind of hung in there to give ourselves a chance to pull off a great result but ultimately they're a good team and we didn't finish the game off," Postecoglou said post-match.
"Credit to players, Leverkusen are a fantastic team and we came to their backyard and gave them a game.
"We just hung in there. We weren't able to control the game like we wanted to.
"We got our goals but just couldn't hang on in the end which is disappointing for the players - they put in a massive effort. But there's still a gap between us and them and that's what we need to bridge.
"In all our European games we've taken it to some very good opponents. They knocked us off 4-0 at home, we've given them a bit of a fright here, so hopefully next time that gap is even smaller."
While Celtic's hopes of Europa League progression are now over, Postecoglou's side are currently second in the Scottish Premiership and will host Aberdeen on Monday morning (AEDT).