I wonder if there’s a bit more too it to be honest. Mourinho’s saying that because of the injury he’s not quite up to the level of intensity needed or training at the level required. It’s probably half mind games aimed at making sure he’s chomping at the bit for when he finally does get a chance/other players lose steam or get injured later in the season.
Then again, it’s also completely possible that either he didn’t want him in the first place, or he’s taking time settling in, like he did at Dortmund, and he simply isn’t good enough yet.