He is being treated with blood thinners and is expected to make a full recovery.
He will miss the rest of the season, however.
Varejao was already out with a knee injury sustained Dec. 18 vs. Toronto. He underwent surgery on Jan. 10 to repair a split in a quadriceps muscle and was expected to miss six to eight weeks.
The 6-foot-11, 260-pound Brazilian has appeared in just 81 games over the last three seasons, having also suffered a fractured wrist and a tendon injury in his ankle.
This season, he was averaging career highs of 14.1 points, 14.4 rebounds and 3.4 assists.
“Clearly our players’ health is our top concern and we are disappointed for Anderson and his family,” Cavs General Manager Chris Grant said in a statement. “We know what a competitor he is and how much he wants to be on the court helping his teammates. In the meantime, he has our full support and we look forward to welcoming him back as he recovers.”