Schaars has not featured for Phillip Cocu's side in 2014-15 following another knee problem earlier in the season, but was on the road to recovery.
The 30-year-old had made two appearances for the club's reserve team in November, but suffered a further problem prior to a clash with RKC Waalwijk and PSV have confirmed he faces further time on the sidelines.
"Stijn Schaars is expected to be out [for] a few months", a statement on Wednesday read.
"Because the complaints to his left knee has not improved sufficiently with rest and customised training, we held an exploratory operation whereby a meniscus problem came to light.
"The keyhole surgery took place last Tuesday, after a period of rest and adequate training.
"Earlier this year Schaars had an operation in the United States because he had been struggling with problems to his knee."
In Schaars' absence, PSV have won 12 of their 15 league matches this season to give them a one-point advantage over Ajax at the top. Cocu's men have also qualified for the UEFA Europa League knockout stages – where they will face Zenit.
