The Mexican forward became a fan-favourite at Manchester United after signing from CD Guadalajara in 2010.
'Chicharito', as he is known, would go on to score 59 goals in 156 appearances for the club before departing for Bayer Leverkusen in 2015.
The 29-year old returned to the Premier League yesterday after signing with West Ham United, but Mourinho says while United still respected their former player, they were not in need for a striker after acquiring Romelu Lukaku from Everton.
"I would always welcome him in my squad because he doesn't need many minutes on the pitch to score," said Mourinho.
"But we move in another direction in a younger player in Lukaku and we have Rashford who can be a striker, so we didn't feel that need.
"But no doubt from West Ham to get a player of his experience and quality is very good."