United hit the woodwork twice in a dominant first half, but they were outplayed after the interval and could have few complaints about Lang's dramatic victor.
That escape was the signal for United striker Zlatan Ibrahimovic to come on in the 74th minute, for the second appearance since his return from a serious knee injury.
Mkhitaryan, 28, was left out of the squad that defeated Newcastle 4-1 at Old Trafford on Saturday and the Armenian cut a lonely figure at training this week. Paul Pogba also returned from a long-term injury.
Bailly's endured a stop-start opening to United's campaign and he will miss tomorrow's trip to Basel in the Champions League. "We don't have Jones, we don't have Eric Bailly again, so Smalling has to play every match and well, that we can say".
"If we are in a winning position, like we were against Newcastle, we need him on the pitch, because he keeps the ball, he keeps possession".
Romelu Lukaku endured a quiet night but he nearly risked the wrath of his manager when he lost possession and Luca Zuffi fired narrowly wide. "But [he is in] no condition to start".
As for Phil Jones, he's been out of action since he went on England global duty.
United's frustration in front of goal showed no sign of subsiding after the break, as they struggled to craft chances against a Basel side who made a marked improvement and even hit the crossbar through Lang.
"I was surprised", Smalling admitted to the gathered press in Basel.
"In some positions where you don't have injuries, you don't have options, and always the same players are playing, in the midfield it was the same a bit".
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