The 26-year-old said on Tuesday her left hand had been "badly injured" as she tried to defend herself during an apparent burglary.
Her spokesman initially said the Czech star would take at least three months to recover from the injury to her racket-holding hand, ruling her out of January's Australian Open.
But the latest development - reported by a Czech news website, which cited a surgeon - means she will also miss next year's French Open and Wimbledon Championships.
Writing on her Facebook page yesterday, Kvitová thanked supporters for many "heartwarming messages" following the attack, which happened on Tuesday morning in the Czech town of Prostejov.
Kvitová, who won the ladies single title at Wimbledon in 2011 and 2014, added that the injury to her left hand was "severe" and she was "fortunate to be alive".
"If you know anything about me I am strong and I will fight this," she told fans.
It is understood the intruder posed as a utilities man seeking to read a meter to gain access to the apartment before a struggle ensued.
The knife was reportedly put to Kvitová's throat and her hand was injured as she pulled the weapon away.
The news of the attack came just hours after Kvitová, who is ranked 11th in the world, said on her Facebook page that she would be missing January's Hopman Cup in Perth, Australia as she continues to recover from a foot injury.