The 25-year-old's defender happily posed for selfies with Hertha fans after his stunning second-half free-kick sealed Berlin's 2-1 German league win over Borussia Dortmund on Saturday.
But the left-back was annoyed to discover he had unwittingly posed alongside Frank Scheermesser, an AfD politician, and the party's Berlin branch, who are seeking to promote themselves ahead of September's elections in Germany.
"@AfDFraktionAGH Please delete the photo immediately! You have no idea with whom I let myself be photographed! I distance myself from this!" tweeted the Hertha defender.
However, the tweet was not deleted and after training on Sunday, Hertha's deadball star said he would take legal action because the picture was used without his permission.
"It's an absolute cheek - something like that is not on," he told reporters.
"You think you're doing a fan a favour and then something like this happens. They just used me.
"It's not correct to post something like that.
"I've responded, which was the right move, so let's see how things go in the next few days."
Plattenhardt's club Hertha has said they will support him in the event of a legal dispute.