Posey had two screws inserted into his leg, but should make a full recovery and be ready to participate in Spring Training next year, Groeschner said.
"It's a good prognosis," he said in a conference call with reporters in Milwaukee. "It's a long road from here. He just had a very devastating injury, had to have surgery and has a long rehab process to go.
"We'll see by the end of the summer where he is at," Groeschner said after Posey underwent a 90-minute surgery at a medical facility in Burlingame, Calif.
The procedure was performed by Giants team physicians Dr. Larry Oloff, Dr. Ken Akizuki and Dr. Mike Dillingham, a retired team physician for the San Francisco 49ers, the Giants said.
"It's a good first step in getting Buster playing baseball again," Groeschner said.
The 2010 National League Rookie of the Year also had his ankle joint scoped, but there was no damage found. Groeschner said the ankle might need to be scoped in the future if scar tissue builds in the joint.
Posey was released following the surgery and will spend about three months on crutches, the trainer said.
The screws were placed across Posey's left tibia and fibula, Groeschner said.
"His ligaments were torn so we have to support that ankle and get it in the right anatomical position," Groeschner said in explaining why the screws were needed. "That's the whole purpose of the screws, to put him in the right position."
Posey will have a second surgery to remove the screws in approximately eight to 10 weeks, the trainer said.
Posey suffered three torn ligaments in his left ankle and a broken left fibula when Scott Cousins of the Florida Marlins plowed into him in a collision at home plate. Doctors believe the broken bone will heal on its own.
"We didn't really do anything with that, which was nice," Groeschner said of the broken leg.
Dillingham, the former 49ers physician who was the surgeon to repair Jerry Rice's knee, is a consultant for the Giants and was involved because of his extensive experience with traumatic injuries.
"He has some great experience with his days with the 49ers," Groeschner said. "This is a contact, traumatic type injury. He's had a ton of experience with that. It was a no-brainer to bring him in."
The loss of Posey was potentially devastating to the Giants, a team that already had been struggling to score runs with third baseman Pablo Sandoval on the disabled list since April 30.
Going into Sunday's game with the Milwaukee Brewers, the Giants had scored the third fewest runs in the Major Leagues, averaging 3.47 runs per game. San Francisco had the fourth best ERA in the Majors at 3.23, allowing the Giants to remain in first in the National League West until they slid half a game behind the D-backs on Sunday.
With Posey out for the season, the Giants are using backup Eli Whiteside as the starting catcher. Whiteside has a career batting average of .227 and is batting .176 (6-for-34) this year.
The Giants have used first baseman Aubrey Huff as the cleanup hitter with Posey missing from the lineup. Huff, though, is batting .224 with only four home runs and 23 RBIs in 51 games.
Posey was injured in the 12th inning of a 7-6 loss against Florida when Cousins barrelled into him as the Giants catcher was attempting to catch a throw from right fielder Nate Schierholtz. Posey immediately rolled over grimacing in pain and was helped off the field.
Posey was batting .284 with four home runs and 21 RBIs in 45 games. Last year, when Posey won NL Rookie of the Year, he batted .305 with 18 home runs and 67 RBIs in 108 games after being recalled from Triple-A Fresno on May 29.
Joe DiGiovanni is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.