Sylvester Stallone has sent a message of encouragement to critically ill Broadway star Nick Cordero.

The Rock of Ages performer has been battling the Covid-19 virus since he was admitted to the intensive care unit at Cedars-Sinai Medical Center in Los Angeles, California at the beginning of April.

He suffered two mini-strokes and a series of blood clots that forced doctors to amputate his leg, and recently had a temporary pacemaker fitted due to an irregular heartbeat.

Against the odds, Cordero has woken from a coma and been responding to commands as he continues to build his strength, according to wife Amanda Kloots, who has been updating fans on his progress via Instagram.

In a new video, shared on her page, Stallone reached out with an uplifting message, admitting he sees a similar drive in the stage actor that he modelled his Rocky movie character after - encouraging him to never give up.

"Obviously, you have an incredibly loving wife and beautiful child and I know to have gotten as far as you have gotten - you got what it takes, you have that eye of the tiger, you have that talent, you have that will," he said.

Amanda told U.S. TV show extra the progress Nick has made over the course of this week has made her more optimistic about his future recovery, revealing: "The nurse said to me yesterday, 'We're not pushing him out of the hospital... He's walking out of this hospital'... and I'm like, 'OK, that's right, I like that!'"