However, Mourinho says the pair are part of a squad rotation system at the Theatre of Dreams and say he can't guarantee playing time to either player.
Martial, meanwhile, has started 16 Premier League games but none since February, although he has been sidelined due to injury, with both forwards hoping to be selected for the World Cup.
"The quality, the experience of numerous players, the squad and the stability of the past years, it is a surprise for me that they find themselves in this position".
Rashford had also questioned his future at the club.
"He is the player with more appearances since I arrived at the club".
Reports in France this week claimed Martial had chose to leave Old Trafford after growing frusrated with a lack of playing time, while there have been claims that Rashford is questioning his future.
"No, no, it's just football", Mourinho said.
The Manchester United manager said in a press conference when asked about Martial's situation: "If I was you I would go why [Romelu] Lukaku plays every match, why [Nemanja] Matic plays every match".
"I have dry answers and a dry answer is only eleven can start the match and we are 22". Only 11 can start.
Anthony Martial has rejected a new contract offer from Manchester United - though has not ruled out staying next season. "It would be better for everyone to have only 11 players but it is not possible".
United could add to West Brom's relegation misery when the strugglers visit Old Trafford in Sunday's Premier League clash. City are 13 points clear of United at the top EPL table.
"I am, I am surprised (to see West Brom in the relegation zone)", Mourinho said. I am surprised because of the quality and experience of numerous players and the squad.
True, Rashford will not be guaranteed a place in the Tottenham starting lineup rightaway, but he should know that Pochettino improves young players and gives them chances.
"In our case, we come from a big result and during the week I was trying to fight that result by working well and hard and trying to make the players understand that it is not enough to deserve second".