A few people gathered outside the hospital where Bolsonaro was treated overnight Friday where the scene was calm.
In this photo released by military police, Adelio Bispo de Oliveira, suspected of stabbing Jair Bolsonaro, sits after being detained in Juiz de Fora.
However, it is unknown when the candidate can get out again on the campaign trail or if his injuries will impede his ability to campaign.
O Globo cites a source in the campaign who described the stab wound as "superficial" and expressed optimism about Bolsonaro's ability to recover and continue campaigning.
General Antonio Hamilton Mourao, Bolsonaro's running mate, told Reuters by telephone that the candidate's condition was stable but still worrying.
In a short clip posted to Twitter, Bolsonaro can be seen being carried through a crowd before an unidentified person stabs him in the chest. He suddenly flinches and then goes out of view.
Social media footage showed the apparent attacker being grabbed by several Bolsonaro supporters before the video cuts out.
Officials said Jair Bolsonaro was in stable condition, though his son said he had suffered severe blood loss.
Jair Bolsonaro is now undergoing surgery, BBC reported, after his liver was injured in the stabbing. Nearly dead... His condition now seems stable.
The military police of Mina Gerais told local media that a 40-year-old suspect had been taken into custody.
Dr. Luiz Henrique Borsato, who operated on the candidate, said the internal wounds were "grave" and "put the patient's life at risk".
Police say the suspect who has been arrested, claimed that he was acting on God's orders.
Despite being a long-serving member of congress, he has successfully presented himself as an outsider, untouched by the corruption scandals engulfing so much of the political elite.
Bolsonaro, a far-right candidate for the Social Liberal Party (PSL), is second in the polls to jailed former President Luiz Inacio Lula da Silva, who is barred from participating but will appeal to the Supreme Court.
Note, according to experts, Bolsonaro is the main contender for victory in the presidential election.
On Thursday, Bolsonaro, notorious for making racist, sexist and homophobic remarks, was being led through a crowd on the shoulders of supporters in Juiz de Fora city in the southern state of Minhas Gervais when an assailant stabbed him from the front and he appeared to scream in pain, reports CNN.
"They made Bolsonaro a martyr", said Jonatan Valente, a student who joined a small vigil in Sao Paulo for the wounded candidate. "'I think the left shot itself in the foot because with this attack they will end up electing Bolsonaro'".
Brazil's stocks and currency extended gains after the stabbing as traders bet the incident could boost support for Bolsonaro, who has tapped a University of Chicago-trained banker as his main economic adviser.
The other presidential candidates were also reportedly quick to denounce the attack.
This is not the first time in recent months that violence has touched politicians. No one was hurt.
While he has a strong following, Mr Bolsonaro is also a deeply polarising figure.
BBC reported that Bolsonaro has faced fines and charges for alleged bigoted comments about women, Afro-Brazilians and the LGBT community.