President Jair Bolsonaro announced the 71-year-old Luna would take the helm of Petroleo Brasileiro SA, as the firm is formally known, in a Facebook post in February.
Petrobras shares fell sharply when Luna's predecessor, Roberto Castello Branco, was forced out after the group hiked domestic fuel prices several times in February, angering Bolsonaro.
The central bank's action on Tuesday followed two similar interventions each on Thursday and Friday, the first time this year it had sold dollars in the spot FX market.
"The situation is serious," said Perfeito, who noted that "the central problem is not the lack of money, but the lack of a clear plan" in a country that still does not have a start date for vaccinations against Covid-19.