Massa is recovering from skull surgery following a high-speed crash during last Saturday's qualifying for the Hungarian Grand Prix.
He also suffered some eye damage and remains in AEK Hospital in Budapest.
"The most important thing first: thank God, all news concerning Felipe is positive," Schumacher said Wednesday on the F1 Web site. "I wish him all the best. For reasons of loyalty to the team I cannot ignore this unfortunate situation. But as the competitor I am I also very much look forward to facing this."
Schumacher, 40, who retired at the end of the 2006 season, said he will drive for Ferrari as long as Massa is unavailable.
His debut could come at the European Grand Prix Aug. 23 in Valencia, Spain.
(Editor's note: This story was corrected Aug. 4, 2009, to insert correct date for the European Grand Prix.)