Aston Villa boss Unai Emery says his side may have squandered their chances of finishing in the top eight of the Champions League following their loss at Monaco.
Wilfried Singo headed home the game's only goal on Tuesday night as a below-par Villa were unable to convert their opportunities.
Finishing eighth or above in the league phase of the competition ensures direct qualification for the knockout stage and a win for Villa in Monaco would have meant they had one foot in the next stage.
However, the loss means they will likely need to beat Celtic at Villa Park next week to avoid having to go into a two-legged knockout phase play-off.