Spain international limped off in the 29th minute of Wednesday night's Copa del Rey quarter-final second leg against Real Madrid and initial examinations revealed a hamstring tear.
Iniesta underwent further tests where it was confirmed the extent of the injury and how long the the 27-year-old is likely to be absent for.
The news means Iniesta is likely to miss league matches against Villarreal, Real Sociedad and Osasuna, both Copa del Rey semi-final ties against either Valencia or Levante and possible the Champions League last-16 first leg against Bayer Leverkusen on February 14.
Barcelona also saw forward Alexis Sanchez substituted 11 minutes from full-time on Wednesday night with a shoulder injury and is expected to miss between one to two weeks.
The match at the Nou Camp finished 2-2 with Barca going through 4-3 on aggregate.