Former Celtic captain Scott Brown believes a win for the Scottish champions against Rangers on Sunday could significantly shift the balance of power in the Old Firm rivalry, especially after a difficult week for Celtic manager Martin O'Neill's team. Last Sunday, Rangers secured a 3-0 victory at home in the League Cup quarter-final, and Celtic followed with a 3-1 loss to Ferencvaros in their Europa League opener on Thursday. Despite these setbacks, Celtic currently hold a five-point lead over their rivals in the Scottish Premiership and are heading into Sunday's match at Celtic Park with renewed focus. Speaking on BBC Scotland's YouTube channel, Brown said that if Celtic can secure a win, they would extend their lead to eight points, which he believes would "change the game." He noted that Rangers will be eager to replicate their performance from last week and emphasized the need for Celtic to match their intensity and determination. "Celtic now have had a week to understand how that game went," Brown said. "They are going to have to make sure that they match that energy but also match that willingness to go and win the match." Brown praised Rangers manager Derek McInnes for his tactical adjustments in the first derby of the season, particularly switching to a 3-5-2 formation and directly challenging Celtic's front three. He was surprised by McInnes' bold move, calling him a "very, very good manager" for identifying the right approach. Reflecting on Celtic's own tactics, Brown mentioned that former manager Martin O'Neill was known for using a 3-5-2 formation effectively, but he believes the current squad lacks the specific players suited for that system. Beyond tactical considerations, Brown pointed out that Celtic's struggles against Rangers stemmed from being physically outmaneuvered and having their key players marked tightly. He argued that the team needs more support from players like Benjamin Nygren and Mika Baur to help ease the pressure on Callum McGregor, who has been crucial in Celtic's attacking play. Brown also emphasized the importance of starting strong in the match, noting that Rangers were highly motivated in their previous encounter. "If you can go and win that battle [in the first 15 minutes], you can get the ball down," he said. He urged Celtic to return to their basics, showing the necessary fight and hunger, as he is confident in the team's talent. "You cannot have just one of those days against your biggest rivals, ever," Brown concluded.