Rashford and Herrera both started in Tuesday's (24 October) Carabao Cup fourth round victory over Swansea City but were both taken off after 67 minutes.
The pair were replaced by the key duo of Romelu Lukaku and Nemanja Matic respectively, a decision that prompted some confusion among United fans given their side were already coasting to victory and with such a pivotal fixture just four days away.
But according to ESPN, those changes were both enforced with Rashford and Herrera picking up minor injuries.
The report suggests Rashford complained of a tight hamstring in the first-half of their comfortable victory at the Liberty Stadium while Herrera was left struggling after taking a kick to the ankle following a challenge with Kyle Naughton.
Both were taken off as a precautionary measure and will be monitored by the club's medical staff in the run up to the visit of Mauricio Pochettino's side on Saturday.
Any doubts over Herrera's availability in that contest would act as another desperate injury blow for Mourinho who remains without three midfield options in Paul Pogba, Marouane Fellaini and Michael Carrick.
Nemanja Matic and the Spanish international have been the manager's only real midfield combination available since Fellaini returned from October's international break with a ligament injury, although 21-year-old Scott McTominay offered an alternative option in Tuesday's win in south Wales.
Rashford meanwhile is in the running to start ahead of Anthony Martial in Saturday's clash. The 19-year-old replaced the Frenchman at half-time as his side trailed to Huddersfield Town last weekend, providing a bright cameo in which he scored his side's only goal of the game. The England international impressed again against Paul Clement's side on Tuesday, providing the assist for Jesse Lingard's opener with a sumptuous flick.
Mourinho already has a number of injury headaches ahead of the Tottenham game. Already without three midfielders, Eric Bailly has also been another recent absentee after returning from the international break with a knock. While the Ivory Coast international returned to training this week, the United boss would not offer an injury update on the defender when speaking to reporters on Tuesday night.
Mourinho is confident of having Phil Jones available again however after his quick recovery from a quadriceps injury. Marcos Rojo meanwhile is nearing his return from a serious knee injury although this weekend will come too soon for the Argentina international, with Zlatan Ibrahimovic hoping to return by December.