Jose Mourinho accused his Manchester United players of shooting themselves in the foot as he saw his under-strength team gift Arsenal two goals in a 2-2 draw that extended their winless Premier League run to four games.
United, who started with Paul Pogba and Romelu Lukaku on the bench, showed great spirit to twice come back, with equalisers from Anthony Martial and Jesse Lingard earning a much-needed point.
But, after a defeat at Manchester City and dispiriting draws with Crystal Palace and Southampton, United are now 18 points behind leaders City and actually closer to the relegation positions than they are first place.
United also trail Chelsea and Arsenal, who are now unbeaten in 20 games, by eight points in the battle for a place in the top four.
Chris Smalling slipped at Lucas Torreiraâs 26th minute corner, allowing Mustafi the space to send a free header bouncing into the ground and goalwards.