"He's not moving well," Girardi said. "As you know, he's had some soreness in his leg. There wasn't anything (Thursday) that told me he was moving any different, but if he's not playing and we've got time, we might as well get a precautionary MRI."
General manager Brian Cashman said the team did not have the results of Rodriguez's MRI late Friday night because team physician Dr. Chris Ahmad was away.
Rodriguez was out of the lineup for Friday night's game against the Tampa Bay Rays, but the game was postponed due to rain and will be made up on Sept. 22. He
went 0-for-4 on Thursday night, and is without a home run in his past 85 at-bats, the longest stretch of his major league career.
"It could very well have a factor," Girardi said of the knee issue. "If you don't have your legs completely 100 percent under you, it's gonna factor in. The great thing is he's still been able to be productive, but we haven't seen the home runs."
Rodriguez revealed in late June that he had been playing through the knee injury, which he suffered on June 19 in Chicago.
Rodriguez thought about scoring on a wild pitch during the sixth inning of the Yankees' 10-4 victory over the Cubs at Wrigley Field, but decided against it. And as he was pivoting back to third base, he tweaked his knee.
The 35-year-old Rodriguez is hitting .295 with 13 homers and 52 RBIs in 80 games for the Yankees this season. He is on pace for just 24 homers, which would be his lowest total since 1997, his second year in the majors, when he hit 23.
Right fielder Nick Swisher is also day to day after injuring his left quadriceps on Thursday night as he tried to dig a ball out of the right-field corner.
"I did it (Thursday) on the first play, on the triple," Swisher said. "When I tried to stop it with my foot because I kind of got caught in whether it was going to ricochet off or go down the line. Maybe I was being hard-headed, but I knew I had it through the rest of the game and instead of coming out maybe I'm paying the price today."
Trainer Gene Monahan told Girardi that Swisher would be out "a day or two." Girardi said that the Yankees don't plan to have Swisher undergo an MRI.
"It's bothering him a little bit," Girardi said. "I didn't see the replay but I guess he tweaked it on a ball in the right-field corner as he tried to stick his leg out to stop it."
The 30-year-old Swisher is batting .249 with 10 homers and 49 RBIs in 82 games for the Yankees this season.
The Yankees also announced they have granted right-hander Brian Gordon his unconditional release. Gordon then signed with the SK Wynerns of the Korean Professional League. The Yankees will get cash considerations from the Wynerns in exchange.
Mike Mazzeo is a regular contributor to ESPNNewYork.com. ESPNNewYork.com's Matt Ehalt contributed to this report.