Roberts, 18, moved from Fulham to City last summer and has spent his time with the senior squad but, after being named on the bench on several occasions early in the campaign, he has been kept out of action with a hip injury in recent weeks.
And despite Kevin De Bruyne's 10-week spell on the sidelines after he damaged ankle and knee ligaments in the League Cup semi-final on Wednesday, Roberts is unlikely to earn many first-team opportunities at City in the foreseeable future and is still set to move to Celtic Park.
"Patrick will go on loan to Celtic – the arrangements were made before this [De Bruyne injury] and we don't want to cut the option to play more games at Celtic," City boss Manuel Pellegrini said on Friday.
"It will be a very important option for him. I am sure that Patrick Roberts will be a very important player here in the future also so to play more games for him at Celtic will be better than to stay here and play just some. We have another young player also who can do it, Brandon Barker - he is a very good player also - so we'll see how many weeks Kevin will be out before he comes back to our squad.
"I think he is all ready to go so I don't think that affects the decision. I think the best thing for the player and the club is for him to go out and play more games."
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The two clubs have been negotiating the length of the loan move and an agreement is thought to be close, although Celtic boss Ronny Deila took a strong stance earlier on Friday, insisting that he will not consider any short-term deals.
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.
"It has to be for longer than a half a season. If not, there is not anything to think about. We have a lot of players. We have to think is it somebody who can make a difference into next season as well.
"We have a relationship with Manchester City – 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 Jason Denayer did and John Guidetti as well then it's positive for both of us.
"Now we know that, if we're going do to things like that, we have to have an arrangement that is over the summer and for a longer period."