In what was a topsy-turvy encounter, Copenhagen scored twice in the final seven minutes, recovering from 3-2 down, to clinch an unlikely victory. Substitute Roony Bardghji netted the winner on 87 minutes, just four minutes after Lukas Lerager had made it 3-3.
United, who had Marcus Rashford sent-off in the first half, raced into a two-goal lead courtesy of a Rasmus Hojlund brace with less than half an hour on the clock. But following Rashford&aposs dismissal in the 42nd minute, Copenhagen fought back to ensure the scores were level at half-time.
Despite being a man light, United restored their advantage with just over 20 minutes of normal time remaining, going into a 3-2 lead via a Bruno Fernandes penalty. A spot-kick was awarded after Harry Maguire&aposs downward header hit an outstretched arm.
United, up until the final 10 minutes, looked poised to record a vital win that would have elevated them to second in the group. Instead, they are now bottom, having lost three of their first four group games.
It means the Reds now face an uphill struggle to escape the clutches of Group A and progress to the last 16 of the competition. MEN Sport has taken a look at the current state of play and what United need to do to keep their European adventure alive.
With two rounds of fixtures remaining, United sit bottom of the group on three points, but only a point behind both Galatasaray in third and Copenhagen in second. Bayern Munich sit pretty at the top of the table on 12 points, meaning they have already won the group with two games to spare.
If the group stays as it currently is, United will exit the competition and play no further part in any European competition this season. Finishing second would, of course, see them progress to the last 16 alongside Bayern, whereas finishing finish would see them drop into the Europa League play-offs.
Looking at the worst-case scenario first, if United lose to Galatasaray later this month they will be out of the competition, regardless of what happens elsewhere. A draw in Turkey would also see United eliminated if Copenhagen beat Bayern.
If United win in Turkey, however, they will climb to six points and into second place, provided Copenhagen fail to beat Bayern at the Allianz Arena. A shock win for Copenhagen will take them to seven points, leaving United a point behind them if they also win.
Put simply, United will qualify for the last 16 if they win their last two games, so long as Copenhagen do not win both of their two remaining matches. Copenhagen host Galatasaray in their final group game on December 12.