Having been beaten late on at AC Milan a fortnight ago, the Bhoys lost 1-0 to La Liga champions Barcelona on Tuesday night at Celtic Park in a controversial match that saw captain Scott Brown sent off.
While he admits that things haven't been going the Scottish side's way in the competition, Commons knows that Celtic's upcoming double-header with Ajax is crucial.
"It is a disappointing result," Commons told reporters. "There's a few things that didn't go our way, a few missed chances that we didn't take but those are the fine lines at this level. We knew we weren't going to have much possession and the idea was to get Sammy [Giorgios Samaras] into the channels and try and get the ball up to the other end of the field as much as we could.
"It was a world-class save from [Víctor] Valdes from James [Forrest] but our best chance fell to Charlie [Mulgrew] and if that goes in the back of the net with 20 minutes left, you never know. For us to have any chance of progressing we need to beat Ajax both home and away."
Celtic host Motherwell on Saturday in the SPFL.