On Saturday in New York, Nix underwent an MRI exam that revealed the strain, which he suffered in Thursday's 6-0 loss to the Blue Jays at Rogers Centre.
"It does affect us because he's a guy that's played second, third, short for us," Yankees manager Joe Girardi said. "We'll have to see how he is when we get back, and maybe he could progress a little bit quicker than that. We'll just have to see."
With Nix out of action, Eduardo Nunez may have just locked up a postseason roster spot. Nunez becomes the Yankees' primary backup at second base and shortstop, while Eric Chavez is the backup at the corner-infield positions.
Though Nunez was with the club as a utility man earlier in the season and played some outfield, the Yankees abandoned that experiment in May and wanted Nunez to focus on playing shortstop in the Minor Leagues.
Girardi acknowledged that Nix's injury should really affect only the last four games of the regular season, since Nix wasn't expected to start in the postseason.
But the manager said that Nix, who has batted .243 with four homers and 18 RBIs in 74 games this season, still could have played a role for the Yankees.
"If someone was to go down or you wanted to pinch-run for someone, [he's] a guy that could really play all over the place," Girardi said.