Anthony Martial arrived at Manchester United's training ground on Friday after his early departure from the club's tour of the United States.
Martial started the opening two games of United's pre-season tour before being allowed to leave in order to attend the birth of his second child.
However, Jose Mourinho criticised the France international for not immediately returning to the tour after the birth.
"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," said the Portuguese.
In a post on Twitter, the French forward wrote: "Thank you all for your posts. My little Swan is fine, for the mum it was harder but thanks to God she's better now.
"Sorry but my family will always come first... Back tomorrow in Manchester."
United face Bayern Munich in their final pre-season friendly on Sunday before they start their Premier League campaign at home against Leicester on August 10.