GRAEME MURTY bolstered the Rangers defence, strengthened the midfield and supplemented the attack with his five January signings.

But it is the deal for the man that will be by his side on Sunday rather than those on the park that has arguably been his shrewdest and most successful at Ibrox.

Jimmy Nicholl was the first arrival of the window for Rangers. While those that followed – Russell Martin, Sean Goss, Greg Docherty, Jamie Murphy and Jason Cummings – have made positive first impressions, the Northern Irishman’s impact cannot be understated.

Read more: Archie Knox: Win over Celtic would boost Graeme Murty's chances of holding onto Rangers reins​

Murty and Nicholl knew little about each other on a personal or professional basis just weeks ago but they will stand shoulder to shoulder against Celtic and attempt to lead their side to Old Firm victory this weekend.

It is Murty that will have the final say and will ultimately rise or fall on the basis of those decisions on derby day. It is a team effort, though.

Archie Knox partnered Sir Alex Ferguson at Aberdeen and Manchester United, was right-hand man to Walter Smith during the nine-in-a-row era and represented club and country with distinction during a glittering career in the dugout.

And the 70-year-old reckons Nicholl’s influence as assistant manager will be crucial for Murty and for Rangers once the whistle blows at Ibrox.

“Graeme couldn’t have a better lad beside him, there is no question about that,” he told SportTimes.

“Jimmy experienced the game as a player, Walter and myself never had that experience.

“He will be a major help to Graeme in the lead up to the game and during the game.

“You are under pressure but you have still got to be calm in terms of what you are doing and what you are seeing on the pitch and dealing with what is happening on the pitch is the most important thing.

Read more: Pressure is on Celtic when they face Rangers -Kris Commons

“Whether it is looking at their weakness or your weakness, you have to look at your players, there might be someone that is having a great game or a poor game, do you need to make a substitution or a change?

“These are all the things that normally go on in a game but the significance of the Celtic game means there is more pressure in terms of doing that.

“I don’t think there is any doubt that Jimmy is best signing Graeme has made. Jimmy will just be working away in the background and doing his own thing but he will always be there if Graeme needs anything.”

The Old Firm showdown on Sunday will be Nicholl’s first derby clash since he moved to Ibrox for a third time and agreed a deal to be assistant manager until the summer.

The 61-year-old has huge experience on both sides of the white line and Murty has often spoken about the qualities that he has brought to his coaching staff.

Victory over Celtic could hugely significant for Rangers and potentially set up a thrilling finale to the campaign.

Read more: Archie Knox: Win over Celtic would boost Graeme Murty's chances of holding onto Rangers reins​

The occasion is anything but ordinary but Knox believes retaining a sense of normality is key to earning a result in the biggest game of the season.

“I don’t know what Jimmy does with regards to training,” he said. “But we were always the same, Walter would do his bit at training and I would do my bit whilst he chipped in.

“We just kept it the same before the Old Firm games, it was the same routine all the time.

“But you could always feel there was a bigger build-up to these games than some of the other games obviously.

“People would be on to you, people in the street, telling you ‘we need to win’. That is the way it was. We had a fair bit of experience of that but it was definitely the biggest game of the season.

“If you know Walter, you know that he could handle all of that. I don’t know if you are surprised to hear it, but it was just a normal routine.

“Obviously you felt a few more nerves in these games, and that was the players and ourselves. You were right up for these games and whatever you could do to help you would.”

Read more: Pressure is on Celtic when they face Rangers -Kris Commons

Murty has already earned points and plaudits against Celtic after leading his side to 1-1 and 0-0 draws on his two trips to Parkhead as caretaker boss.

But the visit of Brendan Rodgers’ side this weekend is the most important afternoon of his managerial career as Rangers look to move within three points of top spot in the Premiership.

It is a day when history can be written and when heroes can be made. It is one that Knox always relished.

He said: “One of the games, the nine-in-a-row game at Parkhead, Brian Laudrup always reminds of it.

“He said ‘I am looking at all you guys, international players…’ and I said ‘well, you will have played in some big games, but you will have never played in one as big as this’.

“Laudrup always reminds me of that and says it was another bit of pressure just as we were taking the field.

“It is not just another game of football. It is against Celtic, your arch-rivals, so it takes on an extra significance, there is no question about that. You feel the pressure that bit more.”

Rangers head into the third Old Firm encounter of the campaign having been on the wrong end of a clean sweep last term and with the 2-0 defeat at Ibrox in September still fresh in the memory.

Read more: Archie Knox: Win over Celtic would boost Graeme Murty's chances of holding onto Rangers reins​

Sunday presents Rangers’ best chance of a derby win for quite some time but Knox knows Celtic will travel across Glasgow in equally high spirits.

Knox said: “The one thing about it all is that Celtic have handled all of that and they have coped with that in the games with Rangers.

“They will go about their business in the usual manner and will say ‘we have done it before, we have coped with all of this before so we can deal with it again’.

“They certainly have the players to do that but Rangers will fancy their chances this time around.”