Demichelis gave away a penalty and was sent off in the 2-0 loss.
"I have seen the moment again on TV and think 'why did I have to tackle him and not keep running by his side?'", he told The Sun.
The 33-year-old added: "I was sure that I would get the ball when I made the tackle. And then you think that you will steal the ball from Messi, you realise that you don't. But I made the foul."
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