Indigenous leader Raoni Metuktire, one of the Amazon rainforest's best-known defenders, is "stable" after receiving a blood transfusion in hospital, his institute said Sunday. Raoni, a chief of the Kayapo people in northern Brazil, has been hospitalized since Thursday for weakness, shortness of breath, poor appetite and diarrhea. "The chief has a stable condition after receiving a blood transfusion," the Raoni Institute said. The institute, which is the Kayapo tribe's official environmental protection organization, said Raoni is undergoing tests to determine the nature of the "digestive bleeding" suspected to be causing his discomfort. Raoni first was transferred to the Santa Ines Hospital in the small town of Colider in Mato Grosso state. The hospital said he was likely suffering from a digestive hemorrhage. He was tested for COVID-19, and the results came back negative. Raoni, now in his 90s, then was transferred to Dois Pinheiros Hospital in the city of Sinop on Saturday due to weakness and a worsening condition. Dois Pinheiros said it would run tests to see if Raoni might be suffering from a gastric ulcer, estimating that he would remain at the facility "at least three days." Known for his colorful feather headdresses and the large disc inserted in his lower lip, Raoni has traveled the world raising awareness of the threat posed by destruction of the Amazon. The president of French NGO Planete Amazon reported that Raoni had been depressed after losing his wife of more than 60 years, Bekwyjka, who died in June following a stroke. He "started to be sick 15 days ago with fever, diarrhea and vomiting" and was very dehydrated, said Gert-Peter Bruch, the association's leader.