Ibrahimovic was a surprise omission from Mourinho's starting XI on Sunday, with club's top goalscorer this season dropping to the bench in favour of Marcus Rashford.
The 35-year-old Swede had hinted in the build-up to the match that he is beginning to feel the effects of a hectic schedule in his first season in England, with 44 appearances and 28 goals under his belt already.
United's most realistic chance of qualifying for next season's Champions League is by winning this season's Europa League, and the Red Devils face a crucial quarter-final second leg against Anderlecht next Thursday at Old Trafford with the tie poised at 1-1.
Mourinho is determined to avoid seeing Ibrahimovic burn out at a crucial stage of the season, saying: "He's tired - very tired.
"I’ll try to protect him but let’s see the result. He's on the bench and ready to help."
Ibrahimovic had told the Daily Telegraph of United's fixture list: "We have one month to go, it's many games we play.
"I have been playing almost all the games. But we are still grinding, we are still pushing because we have this Europa League and the end of the Premier League. We fight for it."
Man Utd XI: De Gea, Valencia, Bailly, Rojo, Darmian, Fellaini, Ander Herrera, Pogba, Lingard, Rashford, Young
Subs: Ibrahimovic, Carrick, Blind, Romero, Mkhitaryan, Shaw, Fosu-Mensah
Chelsea XI: Begovic, Azpilicueta, Luiz, Cahill, Moses, Kante, Matic, Alonso, Pedro, Hazard, Costa
Subs: Fabregas, Zouma, Loftus-Cheek, Willian, Batshuayi, Terry, Eduardo