However it is claimed that that fee raises to 40 per cent if Real Madrid sell to Manchester United.
It’s suggested that the large addition would all but stop a sale to Manchester United with Real unlikely to want to part with such a big percentage.
There is no buy-back clause for City though the current Premier League champions would reportedly be notified of his availability if he does leave the Spanish capital.
Diaz is represented by Pep Guardiola’s brother, Pere.
And transfer expert Duncan Castles spoke about the transfer earlier this week.
Brahim Diaz has reportedly left Manchester City for Real Madrid (Image: GETTY)
Brahim Diaz is unexpected to join Manchester United in the future (Image: GETTY)
"Diaz felt he wasn't getting enough opportunities to play in the first team or develop in the first team, and there's been a lot of interest in his services subsequently," Castles told the Transfer Window podcast.
"He's now agreed personal terms with Real Madrid and will join them.
"I think Manchester City have actually been quite lucky here because Diaz could go for essentially nothing when his contract expires in the summer.
"Madrid would be liable to pay FIFA training compensation of a few hundred thousands euros but Madrid and the player want to make the deal happen in January.
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Manchester City are reigning Premier League champions (Image: GETTY)
"Diaz wants to get out and he wants to play so he's pushing for the move to happen and Madrid, from their point of view, want to announce the transfer and have something to show in the January window.
"They've offered €10million as an immediate transfer fee to City, who have asked for €20m. It looks like it will be settled halfway between them.
"It's not determined yet but City are definitely going to get a reasonable chunk of money for a player who is extremely talented and who will probably be worth a lot more down the line.
"But they have dodged the bullet of the Paul Pogba situation which is having one of your top academy players poached by a leading European rival for essentially nothing."