All 32 teams are required to play at least one game on Thursday Night Football this season just four days after playing on Sunday.
"I think you're taking away from what you're saying a little bit as far as player safety goes," Greenway told the St Paul Pioneer Press.
"Trying to get yourself ready for a game in four days is difficult. I don't care about what level you're talking about."
The Vikings play this week on Thursday night against the Washington Redskins.