Guerrero's wife, Roxanna Jimenez, said Tuesday that "Pedro suffered a massive stroke but he has improved in the last hours."
Guerrero was admitted to the Lenox Hill Hospital in Manhattan on Monday night.
"He's in a critical condition. But he's alive," Jimenez said. "Doctors are waiting for the blood pressure to improve to take the [ventilator] off so he can breathe on his own."
Jimenez said that at around 6 p.m. on Monday, they were in their car on the way to the gym when Pedro started feeling ill. Emergency responders took him to the Jamaica Center Hospital. He was then transferred to the Lenox Hill Hospital, where a bypass procedure was performed within his skull two years ago.
"Initially, doctors told me I should sign a document and get him disconnected from the machine and declare him [dead]," Jimenez said. "But I refused until I learned more about his affliction and after I spoke to the doctor that operated on him in Manhattan. Thank God we made the right decision.
"It was his second massive stroke," Jimenez told the Dominican Republic-based radio show Grandes en los Deportes. "He's recovering. The doctor said he can improve. He opened his eyes and is trying to communicate."
Some of Guerrero's former Dodgers teammates recalled how he had overcome that earlier stroke in recent years.
"He recovered from that, so God willing, he'll recover from this,'' said Steve Yeager, co-MVP of the 1981 World Series. "He's too young to have this happen to him.''
Guerrero was hospitalized in the Dominican Republic in 2015 for bleeding on the brain.
A five-time All-Star, Guerrero had a .300 career batting average with 215 home runs and 898 RBIs.
Orel Hershiser was called up to the Dodgers in 1983 to begin his major league pitching career, and Guerrero played behind him. Hershiser saw Guerrero last year at an alumni game at Dodger Stadium.
"It seemed like he had softened a lot, he was a kinder, gentler spirit,'' Hershiser said Tuesday. "It's sad for me to hear about what's going on now because it seemed like he was really contributing to everyone around him and the lives of everyone around him, bringing them a lot of happiness.''
In 1981, the Dominican earned a spot in right field when Reggie Smith was out with an arm injury. Guerrero was hitting .325 and the Dodgers were leading their division when a players' strike stopped the season in June. Play resumed in August and Guerrero's average dipped to .269 in the second half while the team slumped.
But the Dodgers rallied to win playoff series against Houston and Montreal. They advanced to meet the Yankees in the World Series for the third time in five years.
Guerrero's five RBIs in Game 6 led to a 9-2 victory and the team's first championship in 16 years.
"His career wasn't that long, but he certainly did damage in the time that he played,'' Cey said.
The Associated Press contributed to this report.