Sportsmail understands it therefore results in a one-game ban, a suspension which has now been transferred to England.
The FA say Xherdan Shaqiri was put in a similar situation when the Switzerland midielder moved from Inter Milan to Stoke in 2015.
Pogba's ban means Mourinho will have to wait until next Friday's game at home to Southampton for an opportunity to pick the player as part of his match day squad.
The Portuguese boss confirmed in his pre-match press conference he had found out on Wednesday that Pogba would not be available this weekend.
On Pogba's ban, Mourinho said: 'I don't speak about him. He's suspended and I don't speak about suspended players or injured players.
'I speak about the ones that are ready to play, so I forget Paul for a few days. On Tuesday, he will be ready to play.'
Expanding further, Mourinho said: 'I knew the situation with the yellow cards but I didn't know at that time if an accumulation of yellow cards would bring a player to suspension.
'I didn't know if the suspension would be in Italian football, a suspension for the same competition, or the correspondent competition in England, the FA Cup.
'I didn't know that, so I was waiting for the decision.'
Pogba has been based at United's training ground this week and has revealed he wants to help his new club get back to the top of the pile in England when he is allowed on the field.
The man who left United for Italy in 2012 told adidas: 'I'm feeling good. I can't wait to get back playing, seeing the guys again at the training ground and meeting the players. I really look forward to working with the manager too.
'I want to help get United back to the top and win the league. I didn't win the league when I was back here, and I want to do that because I've never done that.
'I can't wait to make the fans happy.'
Pogba helped France to the final of Euro 2016 earlier this summer and has been enjoying a prolonged holiday following his tournament display.
The box-to-box midfielder knows many of his United team-mates well from his previous spell at the club and said: 'It's great. I spent most of my teenage years here, so it was part of my growing up.
'I remember it all and particularly at the training ground - the changing room, the canteen, the pitches. I'm happy to be back and can't wait to get playing. The people here are so open and friendly too.'
United won the FA Cup last season but it wasn't enough to keep Louis van Gaal in the job with Mourinho swiftly taking over at Old Trafford.
Pogba is used to success with Juventus and helped the club to four Serie A titles, two Coppa Italia wins and two Italian Super Cup successes in his time at the club.
'I had a great year last season and I want to do even better this time,' he said.
'I want to work with the manager and I'm sure he will give me more positivity and more energy to my game.
'I'll be wearing the No 6 shirt. It was one I used to wear when I was in the youth teams before, and one I've had at Juventus and for my country.
'I'm back and I'm ready to start playing football for Manchester United again.'
