Greiss played for San Jose during the Sharks' pre-season games ahead of the 2007–08 season, though he was eventually assigned to the team's then-American Hockey League (AHL) affiliate, the Worcester Sharks. On 8 January 2008, he was recalled to replace German compatriot Dimitri Pätzold as the backup goaltender to Evgeni Nabokov. Greiss started his first career NHL game on 13 January 2008, an eventual 4–3 overtime loss to the Anaheim Ducks. For the 2009–10 season, he served as the back-up goaltender to starter Nabokov.