We don't know if he will play
The Red Devils headed to Portugal on Wednesday night as they looked to continue their excellent start to the campaign on all fronts, but it was certainly a tough test in the Estádio da Luz for the majority of the clash against Rui Vitória's men.
It was Rashford who actually made the difference as his free-kick in the 64th minute was taken over the line by Mile Svilar, however Rashford went down in the 76th minute holding his knee before been replaced by Anthony Martial.
United will return to domestic football on Saturday as they make the short journey to the newly-promoted Huddersfield Town, and Mourinho admitted that he is unsure if the 19-year-old will be involved at Kirklees Stadium.
"With Rashford," Mourinho told the post-match press conference. "I thought it was cramp because he was running so much - I thought it was muscular fatigue."
"But no," the manager stated. "He told me he felt something in his knee."
"It didn't look to me like a big thing," Mourinho added. "But we don't know."
Have to fight to win the group
Wednesday night's performance certainly wasn't a stellar one from The Red Devils, but Rashford's crucial set-piece made sure that United are now in the driving seat to win Group A.
United have had three wins out of three thus far which has left them comfortably at the top of the group three points ahead of Basel, there is still a long way to go in the group with three matches still to play and Mourinho stated that they still "have to fight" to come out on top.
“Yes," he said. "Now we have to fight to win the group."
"I think Basel have six points, we have nine," the 54-year-old stated. "We have to go to Basel and, maybe, we have to discuss the first and second positions in the group."
"Or maybe not," Mourinho concluded. "Depending on other results.”