By North-west correspondent Alex Stevens

Patrick Roberts is set to undergo a Celtic medical after agreeing an 18-month loan move to Celtic, Football Insider sources understand.

The Scottish giants threatened to pull out of the transfer unless the Manchester City winger was signed on a long-term loan deal.

A City source has told Football Insider that the two clubs agreed the terms of the deal earlier on Friday and Roberts will fly up to Scotland over the weekend to undergo medical tests and complete the move.

It is regarded as a coup for Celtic that they have landed the highly-rated 18-year-old for 18 months.

Football Insider revealed last week that the two clubs were in negotiations over a January deal for the England Under-19 international, who joined City from Championship club Fulham last summer for an initial £4.5million rising to £11million.

Celtic manager Ronny Deila insisted he would not budge on the length of agreement he wanted despite the strong relationship he personally has with the Premier League big-hitters.

He said: “We will not take a player on loan to have him only until the summer. He would have to be something special. If it’s going to be loans then it has to be longer than just to the summer.

“We have a relationship with Manchester City. It’s a relationship that I have had for many years, since Stromsgodset.

“We trust each other in the way that we have developed players for them and if they can bring quality into our squad — like we did with Jason Denayer and John Guidetti — then it is positive for both of us.

Celtic manager Ronny Deila is targeting Premier League talent in the January window

Loan ranger: Deila wants Roberts for 18 months

“But now we know if we’re going do to things like that, we have to have an arrangement that is over the summer and for a much longer period.

“If that is not the case it will not happen, you have my word on that.”

The teenager is regarded as one of the outstanding players in his age group in the country but has featured just once in the Premier League this season – a four-minute cameo in City’s 4-1 defeat at Tottenham in September.

Roberts has also twice appeared in the League Cup for City, coming on as a substitute in the victories over Sunderland and Crystal Palace.

Football Insider revealed the Manchester City transfer news on Thursday that the Premier League club would have to pay Fulham a £5million windfall if he had joined a Championship club.