Dr. Lee Kaplan performed the surgery at the University of Miami (Fla.) and will oversee the three-time American League MVP's initial rehabilitation in Miami. Rodriguez is expected to be sidelined for four to six weeks, but he should be available for the Yankees' September stretch drive after a brief stint playing in Minor League rehab games.
"There's no doubt we're going to miss him, but we need to find a way," manager Joe Girardi said in a statement after the decision was announced. "As I've said several times already this year, some people are going to have to step up. Up to this point, this team has. We certainly look forward to getting a healthy Alex back into our lineup, because we know what he adds to this team."
Rodriguez played in 14 games after the injury, hitting .321. His .295 batting average this season is second on the team to Robinson Cano (.296).
But Rodriguez's power numbers have been down. He has just 13 home runs and 52 RBIs, putting him on a pre-surgery pace for 24 home runs and 97 RBIs this season. Only his 23-homer, 84-RBI 1997 campaign with the Mariners resulted in lesser numbers.
Rodriguez has not homered since June 11. His current 85-at-bat stretch without a home run is the longest single-season streak of his career without a long ball.
Yankees left-hander CC Sabathia underwent surgery after last season for the same injury, after playing through pain in the second half and the postseason. But he only had to take the field roughly every five days.
Playing third base, swinging the bat, and running the bases every day would present much bigger challenges, said Sabathia, who could tell Rodriguez was ailing.
"You could see when he was running the bases, him trying to slow down was tough," Sabathia said, adding, "Getting started on trying to get ground balls was tough."
The absence of Rodriguez will likely give Eduardo Nunez another opportunity in the spotlight when the Yankees start the second half of the season Thursday at Toronto.
Nunez, who started at third Saturday and Sunday in Rodriguez's absence, started 17 consecutive games at shortstop after Derek Jeter was placed on the disabled list with a strained right calf June 14.
The 24-year-old Nunez hit .339 during that stretch, and now finds himself replacing another future Hall of Famer for an extended period of time.
Speaking before the decision for Rodriguez to undergo surgery was announced, Nunez said he feels more comfortable at shortstop than he does at third, but felt capable of stepping up if need be.
"I feel bad for him getting hurt," said Nunez, who has committed 10 errors this season. "I don't want to [see] my teammates hurt, but if they need me, I can do it."
Rodriguez first hurt his knee in the sixth inning June 19 at Wrigley Field, when he caught the knee as a baserunner at third base on a wild pitch while pivoting back to third after thinking of running home. He ended up scoring one pitch later on a Russell Martin sacrifice fly.
Matt Fortuna is an associate reporter for MLB.com. Thomas Boorstein is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.