The former Hibernian midfielder was presented to Celtic supporters on Saturday.
“Andy obviously needs to look after his own best interests and that’s what I’ve done as well. He’s been fine with me. He is someone I have known a long time and he will respect my decision as well,” said Allan.
“What did he say to me? He just said: ‘good luck...’
“If we played against each other, that would be interesting. I look forward to it.”
Just last week, Halliday spoke to the Record about his desire to have the former Hibs midfielder join him at Ibrox:
“We were both Rangers fans so we dreamed about it – luckily I’ve achieved it and if it works out the way I want, hopefully he’ll join me.”
The Rangers man hasn’t got his wish and a match-up between the two old pals could well happen in the not too distant future.
The childhood friends went to the same nursery and primary school, lived five minutes away from each other and dreamt of taking to the Ibrox pitch together.
Allan’s future now lies at Celtic Park however, and the Hoops fans have welcomed him with open arms despite his ties to their bitter rivals.
The 23-year old will be hoping to put the controversy behind him and get back to footballing matters as soon as possible, with his next task being to break into a team with the likes of Kris Commons, James Forrest and Stefan Johansen among his rivals for a starting berth.