Leeds United defender Robin Koch will have surgery on Tuesday on the knee injury he aggravated against Chelsea.
The Germany centre-back, 24, was substituted after nine minutes of his side's 3-1 Premier League loss at Stamford Bridge on Saturday.
A Leeds statement said Koch had initially injured his knee during his debut against Liverpool in September.
"Unfortunately, following a collision in the Chelsea game, he suffered further damage to the knee," it added.
"Surgery is required to remedy the problem."
Koch, who joined Leeds from Freiburg in August, has started all 11 of his side's league matches this season.