07/14/2010 at 12:00 AM EDT
On Grey's Anatomy
, Dr. Izzie Stevens has been missing from Seattle Grace Hospital, and now the actress who plays her -- Katherine Heigl
… hasn't been seen at work.
Although Heigl, 31, was scheduled to return to the set
March 1 after three months of maternity leave, “she was not there,” a source close to the situation tells PEOPLE.
Speculation has been mounting that Heigl is off the show for good after six years to focus on her film career. ABC isn't commenting. But Entertainment Weekly
creator Shonda Rhimes
has agreed to release Heigl from her contract, and it's now left to ABC Studios and the actress's rep to work out the final deal.