With the Champions League last-16 first-leg tie at the Etihad finely poised early in the second half, Demichelis was given his marching orders for denying his fellow countryman a goalscoring opportunity - a moment that changed the course of the match.
However, even though much of the City faithful feel aggrieved at referee Jonas Eriksson's decision to brandish a red card, Demichelis believes that the Swedish official was well within his rights.
"I tackled him because I thought I was still outside the box," Demichelis told The Sun.
"But I don't blame the referee. It all happened too fast.
"I have seen the moment again on TV and think 'why did I have to tackle him and not keep running by his side?'"
Manuel Pellegrini's men are certainly up against it after their 2-0 defeat to the Catalan giants, and may have to turn things around in the Camp Nou without their Chilean chieftain on the touchline, as he awaits to hear if he will be handed a UEFA charge for his conduct after the match.
And with Messi in the form he is in, it will be a major surprise if City can somehow manage to progress to the Champions League quarter-final.
"I was sure that I would get the ball when I made the tackle," Demichelis added.
"And then you think that you will steal the ball from Messi, you realise that you don't.
"But I did make the foul."