Smalling hasn’t featured in the first team since Manchester United’s 4-0 defeat at Stamford Bridge back in October due to an broken toe.
Shaw returned in time for Man United’s League Cup clash with West Ham United last month but came off with a knock.
The 53-year-old, speaking after United’s 2-0 win over Zorya Luhansk, confirmed that the pair would not feature on Sunday.
“Not Sunday, no,” he said when asked whether Smalling and Shaw would be returning any time soon.
He provided United fans with some good news with regard to Eric Bailly, who took a nasty knock to the chest on Thursday night, insisting that there were “no problems” with the Ivorian.
“(Bailly) is a big loss but we know that, so let’s hope that Smalling can recover in time to replace him in the squad. With so many matches, we need players. In this moment, I think we have (Phil) Jones, Bailly and Marcos (Rojo).
“Okay, we play Tottenham, we play Crystal Palace, West Bromwich, Reading, semi-finals, West Ham away – in that period we have lots of matches and it’s important to have more options.
“I think (Smalling will be back by the) end of the year, by Christmas.”
Smalling and Shaw, ever since Mourinho publicly questioned their attitude following United’s 3-1 win over Swansea back in early November, have been somewhat lurking in the backwaters at Old Trafford.
The Portuguese, with the pair injured, has channeled his attention towards the likes of Phil Jones, Marcos Rojo and Matteo Darmian – three notably less gifted but perhaps more robust individuals. Their dedication to the cause has clearly impressed Mourinho in recent weeks, and the English pair may have their work cut out when it comes to forcing their way back into the starting XI.