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The real was trading at 4.16 per US dollar in morning trading, within striking distance of its all-time low of 4.2.
Brazil's benchmark Bovespa index also slumped, losing as much as 2 percent in early trading.
On Monday, the first survey conducted since the near-fatal stabbing of Bolsonaro showed him gaining just two percentage points from the previous Datafolha poll, while leftist Ciro Gomes rose to second place, taking 13 percent, up from 10 percent.
Former Sao Paulo mayor Fernando Haddad, who is expected to be named as the candidate for the leftist Workers Party on Tuesday, jumped to 9 percent from 4 percent in the same poll a few weeks ago.