The Northern Ireland defender was sent north by the Magpies as part of a five-man package on the final day of the January transfer window, but Gers missed the fact he was carrying a long-term knee injury when they failed to carry out a medical.
Ferguson, 23, only checked in to the club's Murray Park training base on Monday after he was finally given the green light to resume action.
Now McCall has revealed the Londonderry-born defender/wide man could make his Gers bow as the Ibrox side look to climb back to the Premiership through the play-offs.
The Light Blues boss said: "I was really pleased yesterday when I saw him training. When you have been out for so long with a knee ligament injury, it's not just the physical aspect but the mental one.
"But he was really positive. I've had a wee chat with him and he's desperate to get involved.
"He's a wee bit away from match fitness and won't be ready to play in the next week or two because he's been out too long.
"But he is mentally in the right place, as in he is here to help, and he could be a welcome addition for the back end of the season."
But Ferguson has been a total flop on Tyneside, and even Birmingham City wanted rid of him when he went to St Andrews on loan.
But the Scottish League - well regarded as being the WORST on world football - could be the place he finds his right level.
Newcastle want him off the books, and Rangers could be the suckers who take him on.
The deal which saw Ferguson, Haris Vuckic, Gael Bigirimana, Kevin Mbabu and Remie Streete swap St James' Park for Ibrox has proved controversial.
So far, only Vuckic has played regularly. Street picked up an injury on his debut against Raith and has not been seen since, while the other three arrived packing injury and fitness issues.
But there was another sting in the tail for the frustrated Gers faithful when they learned the deal included a clause which meant their club would have to give Newcastle owner Mike Ashley a £500,000 cheque if they won promotion.
McCall, though, joked he would be happy to hand over the cash if it meant he had succeeded in reclaiming Gers' top-flight slot.
He said: "It was a surprise to everyone when the news about that came out, because it's quite a lot of money, especially when only one of them is playing.
"But if it was me - and it's not because it's not my money - I'd love to give Newcastle £500,000 because that means we have got promotion."