The teenage midfielder quit Barca for PSG in January, leaving much of the Blaugrana staff furious with the decision.
The 18-year-old is represented by former Barça star Iván de la Peña.
Laporta snapped to Sport: "What happened to Dro was a betrayal. If it had happened to Jorge Mendes had it not been like what happened to the bald (Iván de la Peña). It was a shame and a treacherous stab in the back.
"With the PSG president, we established a market relationship, with more money involved, to maintain cordial relations with Barça, and I am grateful for that. I felt sorry for Hansi (Flick).
"He got a role in the A team at the expense of players who deserved it more because they were more involved in Barça. He is an agent thanks to his history in Barcelona: he had a special relationship with them, and I thought it was a treacherous stab in the back."