Manchester United star Paul Pogba could miss Sunday's Manchester derby.
Pogba played ninety minutes in Wednesday night's comeback win over Juventus.
But the World Cup winner was absent from training on Friday due to what the club are calling a "little injury", according to Sky Sports.
Mourinho said ahead of the session on Friday: "Lukaku is training with the team this morning. We have of course one more session tomorrow, but if the answer is positive, he's ready.
"But in this moment, I can only say he trains with the team. I don't know his answer."