The 45-year-old has been in an induced coma since suffering an accident while skiing off-piste in the French Alps on December 29.
"Dear Michael, my great friend, you helped me so much in my career, and I pray for you every day," Massa wrote on Ferrarri's official website.
"I want to see you stronger than ever, just as always. I give you a big hug."
Massa and Schumacher were teammates at Ferrari in 2006.