I'm not sure it's because of bad blood between Pogba and Mourinho. Mourhino is head coach of one of the most expensive football clubs in the Premier League, let alone the entire world. Pogba was one of the most expensive transfers in football history, and if he is not meeting expectations from a player of his talent, Mourinho is going to let him know. Often times, Pogba seems to lack a sense of energy on the pitch that he had at Juventus. Herrera plays hard and consistently. In terms of skill, Pogba is a much more gifted player, but that's not what Mourinho is looking for. He needs to earn that sport in the starting eleven.