Manchester United will be without captain Wayne Rooney and midfielder Michael Carrick for the Europa League clash with Saint-Etienne on Thursday, while Phil Jones remains sidelined. The trio missed training on Wednesday and Mourinho confirmed at his pre-match news conference that they would not be involved in the first leg of United's last-32 tie against their Ligue 1 opponents.
Defender Jones has not featured since limping out of the 0-0 Premier League draw with Hull City earlier this month, when he sustained a bruised foot.
Rooney and Carrick will sit out as a precaution, with an FA Cup fifth-round trip to Blackburn Rovers and the EFL Cup final against Southampton concluding United's February schedule either side of the return leg in France.
"Wayne and Michael, I don't want to say injuries because I don't think we are speaking about injuries," Mourinho said.
"We are speaking about little problems and protection for these problems, so they are out."
— Manchester United (@ManUtd) February 15, 2017
To offset Jones' ongoing absence, Mourinho revealed Marcos Rojo would be fit to play, having missed out on the 2-0 weekend win over Watford, but the Argentina defender will not start.
"My team is playing well and I'm going to stick with [Antonio] Valencia, [Eric] Bailly, [Chris] Smalling and [Daley] Blind," he said, confirming his starting back four.
Mourinho conceded United's ambitions amount to more than participating in Europe's second-tier competition but pointed towards the valuable experiences that could be in store for his squad during the latter stages.
"The Europa League is not a competition we want to play in but we show it respect," he said.
"We cannot choose competitions so we play competitions to win. And I think it's also a good way to give the team, as a team, experience.
"I think European experience is always a plus."