Their chance of a domestic clean sweep was snuffed out when they lost to Morton in the Scottish League Cup in midweek but, while Commons owned up to the disappointment they all felt, he said it would be an even greater honour to qualify from a group including Barcelona, AC Milan and Ajax.
The Spanish champions travel to Glasgow for Matchday Two on Tuesday, with Celtic having lost their opener in Milan. Commons conceded that Celtic had been expected to win the League Cup as part one of a treble this season but insisted they would be punching above their weight if they made the last 16 in Europe for the second consecutive campaign.
When asked if that would eclipse a treble, Commons said: "Definitely, because everyone expects us to win the cup. We are the best team in Scotland and that's why the pressure is all on us. But when people saw our Champions League group I don't think anyone expected us to progress. To even get third position is going to be very difficult."
Celtic face Kilmarnock at Rugby Park in the SPFL Premiership today and inevitably there is the possibility of their attention straying to the visit of Lionel Messi, Xavi, Andres Iniesta, Neymar et al. "I don't think it's the fact it is Barcelona," said Commons. "It's anyone in the Champions League: you'd always have your eye on that game whether it is Barcelona, Ajax or AC Milan. It wouldn't be natural not to think about the next game, but if we don't approach Kilmarnock in the right manner we'll get done."
James Forrest has returned to training after being hospitalised by a virus and, if he is free from pain, will return in time for the Barcelona game. Derk Boerrigter and Biram Kayal are also out today because of knocks but should return in midweek. Joe Ledley will miss both matches.
Neil Lennon confirmed an interest in Ajax striker Kolbeinn Sigthorsson. He watched the 23-year-old play against PSV Eindhoven last weekend but was reluctant to discuss him out of courtesy to Celtic's Group H opponents. "Sigthorsson is a player we like but he is contracted to Ajax and I don't want to talk about a player with another club. I am going to look at players between now and January. That will give me an idea of who we might want and let me get the preparation in before the window opens. Peter [Lawwell, the chief executive] hasn't given me a budget but I know what price range we are working in.
"We're looking at January to bring players in for the remainder of the season and to have them bedded in for the [European] qualifiers next summer. We've money to spend, but the club has to look after the future as well. If we didn't have Champions League football this year we would have maybe had to sell another player. That is the difference between Europa League football and the Champions League."
Lennon was pleased to learn that Jackson Irvine has been called up to the full Australian squad for the first time for friendlies against France and Canada. The 20-year-old midfielder is currently on loan at Kilmarnock but will not play against Celtic today.