They sent the third baseman for an MRI late Friday afternoon, the results of which general manager Brian Cashman said will be available Saturday.
Rodriguez then took his own precautionary step, informing Major League Baseball that he will not participate in Tuesday's All-Star Game.
Rodriguez was voted to his 14th All-Star Game, the most among active players, last Sunday. He was the third Yankee to pull himself from the game, joining Mariano Rivera, who decided mid-week, and Derek Jeter, who also informed MLB Friday.
"He's not been moving well," Joe Girardi said of Rodriguez before Friday night's game was postponed because of rain. "He's been sore, his leg has been a little sore. We're doing a precautionary MRI just to make sure."
A-Rod first started feeling discomfort in the knee during the Yankees' series finale against the Cubs June 19 at Wrigley Field. He also has battled a sore left shoulder this season.
Rodriguez hasn't homered since June 11 against the Indians' Mitch Talbot, a span of 85 at-bats, the longest single-season homerless drought of his career. Girardi said that although Rodriguez has been productive during the stretch -- he's hitting .359 (23-for-64) in his last 16 games and .341 (31-for-91) in his last 24 -- the knee could be the reason for the lack of power.
"It could very well be a factor. If you don't have your legs completely, 100 percent under you, it's going to factor in," Girardi said. "The great thing is he's still been able to be productive, but we haven't seen the home runs."
With the All-Star break coming up, Girardi said he wasn't prepared to declare Rodriguez out for the rest of the weekend.
"Let's see what the MRI says and then we'll see how he feels tomorrow," Girardi said. "I'd love to be able to say I'm going to put him in the lineup tomorrow, but I can't tell you for sure."
Swisher held out
Rodriguez isn't the only player banged up. Mariano Rivera, though available, has been dealing with a sore right triceps, a condition he figures might linger the rest of the season. Nick Swisher was held out of Friday's lineup because of a sore left quadriceps.
He said the quad "tugged" at him when he went after Ben Zobrist's first-inning triple Thursday night. "It's a little tight today," said Swisher, who added he hopes to play Saturday.
"Just to spread out our lineup a little bit," he said. "Without having two guys in the middle of your order, we just thought we would get Brett back up there and we thought it just makes our lineup a little bit different. If not, you're going to hit Gardy sixth, probably, and that's something I didn't want to do. I thought he was probably a little more comfortable hitting first or ninth."
Righthander Brian Gordon signed with SK Wyverns of the Korean Professional League in exchange for cash considerations.