The 20-time Grand Slam winner had the initial arthroscopic surgery in February but said he suffered a “setback” with his rehabilitation.
Professional tennis has been suspended since March because of the coronavirus pandemic.
“I will look forward to seeing everyone back on tour at the start of the 2021 season,” the 38-year-old Swiss said.
Federer has not played since losing to Novak Djokovic in the Australian Open semi-finals in January.
He missed the majority of the 2016 season with a knee injury, but returned the following year to win the Australian Open and Wimbledon.
“A few weeks ago, having experienced a setback during my initial rehabilitation, I had to have an additional quick arthroscopic procedure on my right knee,” Federer said on Twitter on Wednesday.
“Now, much like I did leading up to the 2017 season, I plan to take the necessary time to be 100% ready to play at my highest level.”
The ATP Tour is shut down until at least the end of July because of the pandemic, with the US Open scheduled to start on 31 August and the French Open beginning on 20 September. (Courtesy BBC)