The 30-year-old forward was withdrawn early in the second half of Sunday's 1-1 draw with Granada at the Estadio Nuevo Los Carmenes after twisting his right knee in an awkward fall.
Tests on Monday revealed that the former Real Zaragoza and Deportivo La Coruna man had torn his anterior cruciate ligament and would be out for between five and six months.
Lafita has played in all but one of his side's La Liga outings this term, helping Getafe to the relative comfort of mid-table.
However, with question marks over the future of coach Cosmin Contra as well as midfielders Mehdi Lacen and Michel, the injury serves as another headache for the club during the mid-season break.
The trio are reportedly set to leave the club in January for Chinese Super League side Guangzhou R and F, although Contra recently explained nothing had been signed to complete the deal.
