Brazil's President Jair Bolsonaro will miss a planned Amazon summit to prepare for his surgery, according to an aide.
The operation will be the far-right leader's fourth after he was stabbed in the stomach during his presidential election campaign in 2018, reports BBC.
Brazil may send a representative in his place or ask for the summit to be postponed, the spokesman said.
More than 80,000 fires have broken out in the Amazon rainforest this year.
Mr Bolsonaro has drawn intense domestic and international criticism for failing to protect the region, which is a vital carbon store that slows the pace of global warming.
Environmentalists blame policies enacted by the Brazilian president for the 77% increase in fires this year compared with the same period in 2018. They say he has encouraged cattle farmers to clear vast swathes of the rainforest since his election.\
Mr Bolsonaro has accused other nations of colonialism for offering $20 million to help tackle the fires.
His surgery is to correct an incisional hernia and is his fourth operation since the attack.
The surgery is scheduled for Sunday, and Mr Bolsonaro must start a liquid diet on Friday - the day of the regional conference in Colombia. Doctors said he would need 10 days of rest after the treatment.
Speaking to reporters outside his official residence, the president vowed on Monday to defend his Amazon policy "even in a wheelchair" at a UN General Assembly meeting on 24 September.
"I will appear because I want to talk about the Amazon," he said.
The controversial leader was elected to the presidency in October 2018, a month after he was stabbed at a campaign rally.