Brazil striker Neymar suffered a serious-looking left knee injury during his national team's 2-0 loss at Uruguay in a World Cup qualifier.
Uruguay's goals came on a header by Darwin Núnez in the 42nd minute on Tuesday night and a close-range finish by Nicolás de la Cruz in the 77th. It was Brazil's first defeat in 37 matches of World Cup qualifying.
Neymar, a 31-year-old making his 128th appearance for Brazil, left the field in tears after being surrounded by players from both teams. With and without Neymar, Brazil had its worst performance under new coach Fernando Diniz, who will remain in the job at least until next year's Copa America.
"In the short run we need to be realistic, we need to improve," Brazil captain Casemiro said.
"For Neymar to leave the match it is surely something serious. But I hope it isn't at the end. He has had those injuries whenever he starts picking up his pace again, it is hard."
Later on Tuesday, World Cup winner Argentina, which led South American qualifying with wins in its first three matches, was to play at Peru.
Earlier, Venezuela shocked Chile 3-0. Yeferson Soteldo opened the scoring shortly before the break, Salomón Rondón added a goal in the 72nd minute and Darwin Machis put the final number on the scoreboard seven minutes later. Last week, Venezuela had a 1-1 draw against Brazil.
Ecuador and Colombia had a goalless draw, and Paraguay beat Bolivia 1-0 with a goal by Antonio Sanabria in the 69th minute.
Argentina led South American qualifying with nine points entering Tuesday's matches. Uruguay, Brazil and Venezuela had seven points and were separated by goal difference. Colombia had six points, and Ecuador, Paraguay and Chile had four each. Peru had one point and Bolivia had zero.
The next World Cup in the United States, Mexico and Canada will include 48 teams, meaning direct entry for the top six teams in South America. The seventh-place team will contest an intercontinental playoff for a berth.
Two more rounds of South American World Cup qualifying will be played in November. Brazil and Argentina will face off at the Maracana Stadium in Rio de Janeiro on November 21.
