Celtic slipped out of the Champions League after a third qualifying round defeat to AEK Athens on Tuesday evening, after which manager Brendan Rodgers made little secret of his frustration over the club's summer recruitment to date.
Brendan Rodgers side went behind inside the opening six minutes of the game when Rodrigo Galo met a cross in the box and side-footed it past Craig Gordon.
Hoops substitute Scott Sinclair - on for Australia's Tom Rogic - pulled a goal back in the 78th minute but despite a grand finale the visitors could not fashion a second which would have put them through on away goals.
Celtic still have an opportunity to make it into the Europa League, although having lost back to back games for the first time under Rodgers - they went down 1-0 at Hearts in the league at the weekend - their hard week has done little to quell the optimism of arch-rivals Rangers, who are unbeaten in seven competitive games under new manager Steven Gerrard.
"The two seasons I've been here, we've qualified for the Champions League but it's been a step too far this season".
"At this moment in time we're disappointed with the result of the game and the way we went out".
Rafael Nadal too strong for Stefanos Tsitsipas in Rogers Cup final
After that I accepted the situation, just fought back and tried to stay positive. The Rogers Cup staff also organized a special cake for him in the player lounge.
On the game itself, Rodgers blamed soft defending for the exit.
"In the main, there weren't too many opportunities against us but you can't concede that easily and unfortunately it's cost us".
The 27-year-old former Manchester City man had been the subject of a £9M bid from the newly-promoted Premier League side Fulham towards the end of the English transfer window but the move did not materialise before the August 9 deadline.
"You have got a big problem with Dedryck Boyata, who has refused to play for the club", he said.
Boyata's contract with Celtic only has one year remaining, which Sevilla are hoping will help reduce the price of the player, who is reportedly keen to leave the Glasgow club for Sevilla.
Asked if he felt frustrated on a night where defensive inadequacies proved costly, he said: "Yes, of course".