Marcos Rojo then scored an own goal when sliding in on Arsenal striker Alexandre Lacazette, before Jesse Lingard earned United a point when slotting in 13 seconds after the restart. It was a frantic, and at times feisty, encounter, which saw Unai Emery's Arsenal rack up a 20th unbeaten game in all competitions.
"This is a performance of big soul and heart", Mourinho said.
His absence has brought to an end Xhaka's impressive streak of featuring in the past 65 league games for Arsenal, with the last game the Swiss midfielder missed coming in a 2-0 win over Hull City in February 2017.
The Gunners went ahead when keeper David de Gea made a bad mistake - albeit on a greasy surface - after he could only parry Shkodran Mustafi's 26th-minute downward header that Ander Herrera could not clear before it crossed the line.
It's often a tell-tale sign when a visiting player is applauded off the pitch by the home supporters as the United faithful did when Holding made his way down to the dressing room on the stretcher.
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As a corner was floated in, Shkodran Mustafi bullied his way through and powered a header towards goal.
Four minutes later the hosts levelled when Anthony Martial turned home Ander Herrera's cross after Bernd Leno saved Marcos Rojo's cross. "We could have won this match in certain moments, but they equalised very quickly after both our goals".
The Red Devils, on the other hand, have managed just one Premier League win in four games.
Tottenham Hotspur shook off their north London derby defeat by Arsenal with Harry Kane, Lucas Moura and Son Heung-min all on target for Mauricio Pochettino's side at Wembley where new Southampton manager Ralph Hasenhuttl watched from the stands.
Chelsea took the lead early through Ruben Loftus-Cheek but Wolves replied with quickfire goals by Raul Jimenez and Diogo Jota as Chelsea lost for the second time in three games.
"Our injuries are leaving us in a very hard position to manage, and I have to say that some of our players deserve real credit for their team ethic and bravery to be playing in positions that are not natural to them; for example, Scott McTominay and Nemanja Matic playing as central defenders in our last match".