Former Celtic and Rangers winger Barry Robson thinks Neil Lennon's side will run away with the league title unless there is new investment at Ibrox.
Celtic have turned a 15-point deficit in November into a four-point lead over the ailing Scottish champions.
"I think they need the owner to spend a bit of money because they keep relying on the same boys all the time.
"That's why I think Celtic are going to keep pulling away for the rest of this season," Robson told BBC Scotland.
Celtic overcame a stiff test away to St Mirren in Saturday's early kick-off to record their 12th straight win.
Rangers, on the day veteran former captain David Weir said goodbye to the Ibrox club's fans, followed that by dropping a point at home to Aberdeen.
"I think the Rangers players have been really united as a group over the last few years, but they need a bit of help now," Middlesbrough midfielder Robson told BBC One Scotland's Sportscene.
"With the squads at the start of the season, Rangers were punching above their weight in my opinion.
"You can't keep relying on Naismith, McGregor, Davis, big Davie Weir is obviously away now.
"These are the guys who've been doing it for the last three seasons and they need help now and the team badly needs investment.
"You are about to lose Davie Weir, your main character in the dressing-room and you can see what's happening on the pitch because of that."
Robson praised Ally McCoist, who took over as Rangers manager from Walter Smith in the summer, but thought that the Ibrox club needed to end the financial uncertainty resulting from a the court battle over a major tax bill that has cast a shadow over Craig Whyte's takeover.
"More investment would be better for the league and better for the title run-in, because I can see Celtic running away with it at the moment," said Robson.
The player who joined Celtic from Dundee United in 2008 before heading to the Riverside thought the Parkhead club had shown great strength of character to make up ground on their Glasgow rivals.
"They were down and out and so many points behind Rangers," said Robson.
"But I've looked at Celtic and Rangers from the start of the season and I've always fancied Celtic for the main reason that their squad is a lot stronger for me."