"I will be missing my fans and the tour dearly but, I will look forward to seeing everyone back on the tour at the start of the 2021 season."
In February, Federer said he expected to miss only four months of action following the surgery to his right knee.
At the time he was hopeful of recovering in time for the grass court season before Wimbledon and the 2020 Olympics.
Fans reacted with disappointment, with many saying the news has added to an already tough 2020.
Wimbledon has since been cancelled due to the global Covid-19 crisis, while the Tokyo Games have been postponed to next year. Organisers of the French and US Opens are considering ways of staging their respective events.
The latest setback will not do anything to dispel the imminent retirement rumours that have dogged Federer since 2013.
Federer missed the Rio Games and much of the 2016 season due to injuries to his knee and back but returned the following year to complete his most successful season in a decade - including wins at the Australian Open and Wimbledon (his first Slam victories since 2012).
He is currently ranked No 4 in the world, after reaching only one Grand Slam final last year - losing in a five-set thriller to Novak Djokovic in the title-decider at Wimbledon.