He wooed Barton by taking him golfing at luxurious Loch Lomond and flew to New York to convince Kranjcar to make Rangers his next club.
Unfortunately, he has lost the talents of Kranjcar for the rest of the season as a result of a serious knee injury.
And he is unlikely to allow Barton to pull on a Rangers shirt again as a result of his behaviour during a heated training ground row with Andy Halliday in the wake of the 5-1 defeat by Celtic when he is also understood to have undermined the manager.
Rangers issued a statement yesterday stating that the 34-year-old needs to report back to Murray Park following the conclusion of the disciplinary procedure that followed.
In it the club stated Barton “will be informed of appropriate training arrangements to which he must adhere for as long as he remains a Rangers player”.
There is no suggestion that he will re-join his former team-mates or become available for selection again and it smacks of following protocol. The club have a requirement under Fifa rules to offer him training facilities while he remains under contract.
Rangers want him to maintain his fitness levels, especially with the January transfer window fast approaching and a number of English teams, including his former club Burnley, interested in acquiring his services.
Barton is also facing Scottish FA charges for breaching betting rules. He is accused of placing 44 bets on games between 1 July and 15 September – although none of these matches involved Rangers.
He has asked for more time to consider his response to the charge and to examine paperwork in the case against him and the SFA’s judicial panel agreed to postpone the hearing from 27 October to 17 November.
Despite the loss of Kranjcar – whom Warburton insists will make a complete comeback – and the seemingly inevitable departure of Barton, the Rangers manager will trust his remaining players to fill the void.
Warburton said: “Niko has the mental fortitude to come back. Anyone who saw him against Inverness, against Partick [and] anyone who had seen him training will know all his hard work was paying off.
“He was getting stronger and dominating games. He’s got the ability with his technique to control games and he was doing that. Against Inverness he strolled through 75 minutes and that’s the biggest frustration.
“He’s a well-liked guy. The physio said when he got injured on the park it’s the first time he had seen every single player – to a man – come over and check how he was. It shows the respect people have for him.
“It’s a blow. There’s no point masking that. We knew what he could do. We couldn’t predict the timescale it would take for him to get where he wanted but every day he did extra in training.
“He went back to see his family in Croatia and worked with a fitness coach and produced heart-rate data every single day. He was seeing the fruits of that so to lose that calibre of technical player is a blow.
“But from a negative comes a positive and Jordan Rossiter is coming back from injury and Matt Crooks is getting fit. Then there’s the form of Josh Windass, Jason Holt and Andy Halliday. Someone’s pain is someone’s gain.”
Warburton, who is hoping to make it three wins in succession when Rangers play Ross County in Dingwall on Sunday to maintain second place, has reiterated his dislike for the January winter break and revealed why Rangers will travel to face RB Leipzig in a friendly on 15 January.
He said: “I’ve got issues with the three-week break, so we had to arrange a game. We wanted to give the boys five or six days off and then we’ll come back and prepare for the week and we wanted a high-quality fixture in the build-up to our Scottish Cup tie.
“We don’t know yet who we’ll play or whether that game will be a Friday, Saturday or Sunday but we wanted a top-quality fixture and they’re second top of the Bundesliga behind Bayern Munich.
“It’s a fixture we’re looking forward to and, obviously, Ollie Burke is there too and they’re well backed, a wealthy club who are making great strides. It will be a tough test but you have to take yourself out of your comfort zones.”
Warburton also confirmed that Rangers are hoping to tie down 15-year-old Billy Gilmour on a long-term deal with top English sides reported to be hovering. He said: “Billy Gilmour is an outstanding talent so of course our job is to persuade him that it is good for his future to stay at Rangers.”