The midfielder said sorry to all associated with the Blues after seeing red 16 minutes into the game at the Kassam Stadium.
The Welsh ace was dismissed by referee Samuel Barrott for a foul on the U’s’ Cameron Brannagan – a decision that has incensed the Fratton faithful on social media.
The match was tied at 1-1 at the time, after Michael Jacobs cancelled out Luke McNally’s seventh-minute opener.
However, forced to play the rest of the game with 10 men, the brave visitors were unable to maintain the advantage handed to them by Ronan Curtis’ goal on 51 minutes.
Indeed, both Brannagan (82) and substitute Nathan Holland (90+5) struck late in the game to earn the home side victory as the Blues await their first league win of 2022.
Despite not agreeing with the referee’s decision to send him packing, Morrell took responsibility for the role his dismissal played in the result.
And he praised the spirit shown by his team-mates, insisting it will stand Pompey in good stead as they now sit 13th in the league table.
Morrell tweeted: ‘Can only apologise to the fans, staff and lads for today.
‘Needless to say that I didn’t agree with the decision but take responsibility for it.
‘That spirit and togetherness that the boys showed today will take us a long way.’