Former Celtic captain Scott Brown believes a win for the Scottish champions against Rangers on Sunday "changes the game" after a turbulent week for Martin O'Neill's side.
Rangers triumphed 3-0 at home in last Sunday's Old Firm League Cup quarter-final before Celtic opened their Europa League campaign with a 3-1 defeat at home by Ferencvaros on Thursday.
However, Celtic's early season domestic form has them going into Sunday's match in the east end of Glasgow - which like last week will have no visiting supporters in attendance - with a five-point advantage over their Ibrox rivals.
"If Celtic win and they're eight points clear, it changes the game," Brown said on BBC Scotland's YouTube channel.
"Can [Rangers] go to Celtic Park and do they exact same thing as last week?
"Celtic now have had a week to understand how that game went. They are going to have to make sure that they match that energy but also match that willingness to go and win the match."
Celtic seek spark as Rangers aim for further derby joy
Scottish Premiership: Celtic v Rangers
Listen on Sportsound, highlights on Sportscene
20/9/26 from 11:00 BST (radio), 19:15 (TV)
McInnes got it right last week - can O'Neill respond?
Brown was impressed by Rangers manager Derek McInnes' change of approach in the season's first derby, change to a 3-5-2 shape and going man for man with Celtic's front three.
"They went after Celtic from the get go," Brown said. "They looked like they wanted the win more. For him to change his tactics, nobody expected him to do that. That is a very, very good manager to pick that out."
Brown also pondered Celtic's tactical plan.
"Martin O'Neill when he was manager [from 2000-05], loved a 3-5-2 and it was fantastic to watch," said the former Scotland captain.
"He had two big guys up front. That was an unbelievable team. He's not got those players that probably can be suited to a 3-5-2."
With Yang Hyun-jun still on Asian Games duty with South Korea, Sebastian Tounekti and James Forrest have both been used on Celtic's left flank.
But Brown believes the club's problems go beyond that.
"Rangers got in their face, they blocked Callum McGregor off and as soon as you block Callum McGregor off and you man-mark Cal, it's hard for anyone else to go and dictate.
"That's when you need a [Benjamin] Nygren to drop under, a [Mika] Baur to go and drop under and them do their job as well. You can't always keep looking at Cal to do everything."
And Brown believes who starts best could be crucial.
"Rangers were up for the fight," he added on Sportsound. "The first 15 minutes, it should be a battle. If you can go and win that battle, you can get the ball down.
"Celtic started very, very slow last week. They need to go back to basics, make sure they've got the fight, make sure they've got the hunger because they've got the talent - I know they've got the talent.
"You cannot have just one of those days against your biggest rivals, ever."
