By Dominic Toner

Graeme Souness believes that only financial investment will bring Rangers level into the same league as Old Firm rivals Celtic.

Rangers have completed a remarkable return to the Scottish top-flight after their liquidation in 2012.

Celtic have won the last five consecutive league titles and are currently four points ahead of second-placed Aberdeen this season, with a game in hand.

Brendan Rodgers has enjoyed a great start since becoming Celtic manager and inflicted more misery on Rangers at the weekend.

Mark Warburton’s side suffered a 1-0 defeat in the League Cup semi-final, with forward Moussa Dembele scoring a late winner in the 87th minute.

Former Rangers player and manager Souness believes that the club must inject more money if they are compete against their rivals again.

“Celtic are five year ahead, they’ve had a five year period where they could rule themselves,” Souness told Sky Sports. “Rangers have done remarkably well, I think the supporters have done well when you consider how they’ve stayed with the club.

“The gap is there, we have to except the gap is there and hopefully we close that very quickly and that will be done by investment. And that’s down to the owner finding the money for the manager because right now the manager is operating with one hand tied behind his back.”

Rangers were comprehensively beaten in the league meeting against Celtic in September, as they suffered a humiliating 5-1 away defeat.

The Gers completed free transfers for the likes of Joey Barton, Matt Gilks, Jordan Rossitier and Philippe Senderos in the summer window, but Souness feels the club will need to spend some big money to reach the top.

Warburton’s side cruised to the Scottish Championship title last season and have found it much more difficult in the top-flight.

The Scottish giants are currently fifth-placed in the table and are desperate to return the club to its glory days of challenging with Celtic.

In other Rangers news, Warburton has provided a fitness update on Niko Kranjcar’s injury.