Failure to win against St Mirren, Dundee United and, most recently, Motherwell has resulted in the Light Blues slipping four points adrift of Celtic at the top of the Scottish Premier League.

Next up is Saints at Ibrox on Saturday, against opponents who will be bolstered by their shock win at Love Street in early October, and former Rangers star Roberts admits his old club cannot afford a repeat of that result.

"They have to stop dropping silly points to the likes of Motherwell, St Mirren and Dundee United," he said.

"Rangers have to start winning those games so that, when they do beat Celtic, they know they will be top of the league.

"If you don't win those other games then you're going to be in trouble."

Rangers had hoped the one positive to come out of their lack of European football this season would be their ability to focus entirely on the domestic scene.

Last year's epic run which ended in a UEFA Cup final appearance proved too much to cope with on top of their SPL challenge as they lost out to Celtic on the final day.

So far, Celtic have been able to cope with their responsibilities both home and abroad - but Roberts believes there is still time for their European commitments to take their toll.

"I think Celtic will qualify for the UEFA Cup and that will give them a lot more games and it may make it easier for Rangers to push on in the league," he said.

"Rangers have to win the treble this year - that's the way forward for them.

"They are in the semi-finals of the League Cup and have managed to avoid Celtic so they will fancy their chances in that one.

"They also have to win the league and the Scottish Cup."

Roberts believes next month's Old Firm derby at Ibrox will be crucial in the title race as Rangers attempt to overcome that four-point deficit.

"It's big now," he admitted. "They have done the hard one by winning 4-2 away from home at Parkhead but they need to win their home games.

"I would strongly fancy Rangers on the day, I think the players will be up for the game."