Zanchi was brought on in the 80th minute to rapturous applause, after battling back from brain surgery that had threatened his career.
However, the player was stretchered off just two minutes later and will be forced back to the treatment table.
Early indications point to a muscular tear, but Zanchi will face a barrage of tests to ascertain the extent of the damage.
To add insult to injury, Zanchi's injury allowed Lazio to score the winner in a 2-1 victory, which is sure to leave fans wondering if he was rushed back.
