Mark Warburton has confessed that Rangers trail in Celtic's wake when it comes to the financial disparity between the two clubs, but says his side cannot afford to "cast envious eyes across the city".

The Bhoys are storming their way to a sixth Scottish Premiership title in succession, dropping just two points from their opening 19 games to find themselves 16 clear at the top.

Warburton admits that second-placed Rangers must look to close the gap on Celtic in more ways than one ahead of this weekend's crunch derby clash, knowing that bringing in more funds is likely to be the only way to halt their Old firm rivals' dominance.

"The reality of the situation is there is a very evident financial disparity between the two clubs. Champions League football is a huge difference, and what we have to do is focus on Rangers," he told Sky Sports News.

"We can't cast envious eyes across the city. We need to get there. We have to do it in a structured manner, that's key. We can't spend money we haven't got, we're not going to buy our way out of trouble, and that's not a complaint or a moan, that's just reality.

"It's important to be honest about the whole situation, so we know right now there is a big financial disparity that exists and we have to close it in as short a period of time as possible."

Warburton has yet to lose a home match in charge of Rangers since taking charge of the club at the start of last season, but he faces his toughest test yet when Celtic visit on Saturday lunchtime.