Both men were left out of the starting lineup to face West Ham United on Thursday, as Mourinho instead opted to go without a recognised striker through the middle.
Rashford was brought on for the final 16 minutes of the goalless draw at the London Stadium, while Martial was left on the bench for the fourth time in eight games.
Speaking after the match, Mourinho explained his decision to leave out the attackers as two of eight changes from the 1-0 loss at Brighton & Hove Albion.
"Marcus and Anthony played against Brighton. Today was for Alexis [Sanchez] and [Jesse] Lingard; Sunday is a game for Martial and Rashford," he told reporters.
United follow up this weekend's meeting with Watford by taking on Chelsea in the FA Cup final on May 19.