The Scottish champions have endured a gruelling schedule in recent weeks as they attempt to balance their European aspirations with their defence of the title, with both Rangers and Celtic boasting 100% records in the Clydesdale Bank Premier League so far.

Sunday's highly-anticipated trip to Celtic Park comes just days after the visit of the Spanish high-fliers.

But, having emerged from that game disappointed with only a draw, Whittaker is confident Walter Smith's men will be ready for the battle with their greatest foes.

He said: "Now that the Valencia game is out of the way, the next few days will be spent trying to get the energy back in the legs and concentrating on Sunday.

"It's a game we are looking forward to."

Maurice Edu netted for both clubs as Rangers were held to a 1-1 draw against Valencia, having passed up glorious chances to win the match.

"There is disappointment in the changing room and we have just drawn 1-1 with Valencia," said Whittaker.

"That tells the story. We created enough chances to win the game and we are a little bit disappointed.

"We are sitting in a good position and we have definitely improved upon our results last year, which were disappointing.

"We've had a great start to this campaign and we are unbeaten with one win and two draws. We are in there fighting and hopefully we can continue that in the next few games."

Rangers sit second in Group C behind Manchester United, with five points from their opening three games.

"No one has really spoken about where we want to be in the group," said Whittaker.

"We treat every game individually and try to get the best result we can from that game. We will continue to do that and see where it takes us.

"People probably didn't give us a chance before the game but I think we are showing in this campaign that we are capable of beating teams in our group."

Important games keep coming thick and fast for Rangers, who take on Valencia again, this time at the Mestalla, early next month.

Whittaker said: "We frustrated them and they couldn't really come up with the answers to break us down.

"We looked dangerous on the counter-attack and hopefully the game over there will pan out in the same way."