The Scottish defender was a member of the Hoops squad at the time, but was on his way back from injury when the Dutch giants visited Parkhead in Europe.
Unfortunately for Ronny Deila and his team, they were unable to build on a decent performance and ended up losing to 2-1 to Ajax after a Vaclav Cerny winner in the 87th minute.
As the Celtic players walked re-grouped immediately after the goal, Mulgrew was bizarrely seen walking straight off the pitch.
And that left the Scottish champions with 10 men for the final few minutes, killing any chance of a late equaliser.
Mulgrew attracted a lot of criticism for walking off, despite his public clarification that he was injured and couldn’t continue.
Now he’s attempted to clarify the situation further by saying he re-injured his quad and it simply wasn’t possible to carry on.
Speaking in an interview with Si Ferry, Mulgrew said:
It was unusual for Mulgrew to walk off the pitch when he hadn’t signalled to the bench – and it looked more like him walking off in a mood than anything else.
But his explanation for the situation makes sense and should show the Celtic fans that there was a legitimate reason for leaving the pitch.