The Mets said Thursday night that Diaz underwent surgery earlier in the day and is expected to begin a formal rehab program in about a week.
"To all my beloved fans, especially the Mets fans, I want to let you know that I am doing well and healing," he wrote on social media. "I feel blessed and grateful for your support with messages and prayers, thank you very much! I can't wait to see you guys in NY again and play those trumpets."
Speaking earlier Thursday, general manager Billy Eppler said a general timeline for recovery from this type of injury is about eight months.
"There are instances where athletes have come back earlier, more around the six-month mark," Eppler told reporters. "But those are a little bit more of the exception than the rule."
Díaz, who turns 29 next week, retired the side in order in the ninth inning Wednesday of a 5-2 victory over the Dominican Republic that sent Puerto Rico to the WBC quarterfinals. As Díaz and his teammates jumped together in the infield, the right-hander collapsed and reached for his right leg. He was taken off the field in a wheelchair.
"To see him get hurt like that, it's a sad thing for Puerto Rico, for all of baseball," Puerto Rico manager and former Cardinals star Yadier Molina said Thursday. "We wish him the best. We're praying for him, and we know he's going to come out of this stronger."
"Edwin Díaz is a great human being and a fierce competitor," Mets owner Steve Cohen tweeted. "All of us at the Mets are shaken but determined to sustain our quest for a great season. We wish Edwin a speedy recovery."
Eppler said he spoke to Díaz several times and noted that the right-hander was in "great spirits."
"He's a resilient human being," Eppler said. "That's why he's the closer he is. The dude doesn't get rattled."
The Mets signed Díaz to a five-year, $102 million contract -- the largest ever for a closer -- after he produced a spectacular 2022 season. All player contracts are covered by insurance through the WBC that spans the length of time the player is out with an injury suffered during the tournament.
Díaz went 3-1 with a 1.31 ERA and 32 saves in 35 opportunities while striking out 118 batters in 62 innings last season. He made his second All-Star appearance and finished ninth in the Cy Young Award voting.
The Mets do have relievers on their roster with closer experience as they attempt to replace Díaz.
"[Alexis Diaz] is a professional, and he's going to be ready," Molina said.
Puerto Rico faces Mexico on Friday in the WBC quarterfinals. The Brewers' Alex Claudio was added to Puerto Rico's roster and will be available for the game.
Tigers shortstop Javier Baez said Edwin Diaz, nicknamed "Sugar," visited Puerto Rico's clubhouse while the players were awaiting the MRI results to talk to his teammates and try to motivate them for the rest of the tournament.
"We're going to do this for our country, and also for Sugar," Baez said. "I can't express to you what that clubhouse feels like. It feels super motivated by what happened yesterday -- to win for Sugar."
Eppler didn't have details on exactly what caused the injury but said torn patellar tendons happen more often in other sports.
"It's an injury that's actually really common in the NBA and NFL," Eppler said. "When you get excessive load put on your knee, it can happen."
Francisco Lindor, a teammate of Diaz's on both the Mets and Puerto Rico, said he understands how Mets fans are feeling but also noted how important the WBC is to players from his country.
"While for so many people the regular season is what counts, playing in the WBC means just as much to all of us," Lindor told ESPN. "It is the dream of every Puerto Rican ballplayer to wear Puerto Rico's colors and to represent our country. And not only Puerto Ricans, but every player in the WBC considers being here the ultimate honor. Of course, we don't want injuries to happen, but it is part of the game. And they are things that can happen just anywhere. Of course, this is sad for all Mets fans. And I want to thank them for being so concerned about us, and about Edwin, and I really do also feel your pain."
ESPN's Marly Rivera, Alden Gonzalez and The Associated Press contributed to this report.