Morrison will appear in the last few episodes of the current season of the medical drama, reports aceshowbiz.com.
There's speculation that the "Glee" actor will play character Jo Wilson's (Camilla Luddington) abusive estranged husband.
Morrison revealed on his Instagram story that he is playing Dr. Paul Stadler on an unnamed project.
He has also been photographed filming a scene with actor Justin Chambers, who plays Alex Karev, on location here with Kevin McKidd as director.
At the end of season 12, it was revealed that Jo Wilson was reluctant to marry Alex because she was already married. And because she would run away from her abusive spouse, she couldn't obtain a divorce.