Former Celtic midfielder John Collins believes that Gordon Strachan has won the right to be given more cash for players by the club's board.
The Celtic boss is under pressure with his side trailing SPL leaders Rangers.
But Collins told BBC Sport: "He has not spent a lot of money and he has won back-to-back titles and taken them to the last 16 of the Champions League.
"I think it's time for Celtic board to give him a little bit more money to spend in the summer."
The reigning champions visit Ibrox on Saturday three points behind Rangers and having played one game more.
"In the last few years, they have been in front in the title race, so the pressure is on now that they are chasing Rangers," said Collins.
"Trust me, £4.5m for Scott Brown is value for money"
"It's a game they can't afford to lose as to go nine points behind would be very difficult to come back from.
"I don't think there are many points to be dropped elsewhere, so the Old Firm games will decide the title."
Collins thinks it is a difficult fixture to predict.
"Celtic have been creating a lot of chances and eventually that's going to turn," he said.
"Rangers have not been playing great football or winning convincingly, but they have been gathering the points.
"The way that Rangers have had it in the last two or three years without trophies, I am sure their fans will not be bothered."
Collins thinks that Aiden McGeady and Scott McDonald are the key men for Celtic, while Rangers will rely heavily on Jean-Claude Darcheville and Barry Ferguson.
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But he thinks that two players that played for him at Hibernian can also play their part.
"It's never easy in your first season with a big club, but I have no doubt that Scott Brown will be a really good player for Celtic and has the ability to win this game for them," he said.
"£4.5m is not a huge amount to pay for a player these days. Trust me, £4.5m for Scott Brown is value for money."
Brown's former midfield team-mate Kevin Thomson has also had his critics since moving from Easter Road.
"He sits in a holding role for Rangers, but I think he has the talent to do more and get further up the park," added Collins.
"It's an unglamorous role. He just gets the ball and plays simple passes for the team, rarely gives the ball away and does it very well."
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