The Hoops played their third Europa Leauge group stage game against Sparta Prague at Parkhead on Thursday and succumbed to a 4-1 defeat.
Having lost two and drawn one of their Europa League group stage matches so far, Celtic have no chance of progressing into the next round, former goalkeeper Bonner believes.
Celtic could still potentially reach ten points in the group, which could be enough to see them qualify, depending on other results, but Bonner thinks the focus must now be on the Scottish Premiership.
Bonner is of the view that Rangers could establish their lead at the top of the table further in the upcoming weeks and urged Celtic to get a winning run going to catch up with their arch-rivals.
“Rangers can take a real grip on the league over the next few weeks“, Bonner told BBC Sport.
“This will be a major blow for Celtic. They need to get a run going somehow.
“They’re out of Europe now, they have to put all their focus on the league.”
The Celtic legend also stressed that the pressure is on Bhoys boss Neil Lennon.
“This is a real challenging time for any manager and he’ll have a few sleepless nights.“
Celtic are currently nine points behind table-toppers Rangers, although they have two games in hand.
