"The initial diagnosis show that he had injured cruciate ligaments in his knee," Spartak said on their website.
The 30-year-old Croatia international will have surgery in Germany on Sunday.
Pletikosa, who was Spartak's starting goalkeeper for the past two years, has been looking for a new club after being relegated to the bench this year.
"Spartak have informed English club Tottenham Hotspur, who have shown a great interest in acquiring (Pletikosa), about his injury," Spartak said.
Pletikosa is certain to miss Croatia's next two World Cup qualifiers against Belarus and England on Sept. 5 and 9 respectively.
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