Martial left United's pre-season tour of the United States on Wednesday to be with his partner in Paris for the birth of their second child.
But just three days later the United manager has criticised his player for not immediately returning to Michigan for the friendly fixture against Liverpool.
Anthony Martial has the baby and after the baby is born – beautiful baby, full of health, thank God – he should be here and he is not here.
“Now we have Real Madrid and after that we have Bayern Munich and that’s our start," Mourinho continued.
“I just hope the boys on deserved holidays, they take care of themselves a little bit and somebody wants to do what Rashford and Jones do, which is to be back a little bit earlier to try and help the team because, for the beginning of the season, we’re going to be in trouble.”
Martial's partner, Melanie da Crus Pires, confirmed the baby's safe arrival on Friday.
Martial has yet to respond to his manager's comments, while Manchester United were unable to confirm that the player had been given permission to attend the birth.
Speaking earlier this week, Mourinho suggested that he had not been party to the decision for Martial to leave the pre-season Tour, saying:
I found out that Martial was going to Paris when he told me. It was two or three days ago.
"When it is personal reasons, everyone analyses that the way he thinks is the correct way. When a man is going to be a father — in this case, it's the second time he is going to be a father — and he decides it is very important for him to go, nobody has the right to stop him to go."
United have two more scheduled pre-season fixtures, against Real Madrid and Bayern Munich, before their Premier League season begins against Leicester City on Friday 10 August.