The Bills host the New England Patriots in their opener on Sept. 8.
"Right now we're planning on Jeff Tuel playing the first game and we're working with EJ to get back as quickly as possible," Marrone told reporters, according to the team's website. "Meaning New England. Right now that's how we're going about planning on doing it until we know more about where EJ is."
If Tuel does indeed start in Week 1, he will become the first undrafted rookie quarterback in the common draft era (since 1967) to start a season opener, according to the Elias Sports Bureau.
"That's cool," Tuel said, according to the team's website. "It would definitely be an honor if that's the case. I'm surprised that I'm the first, but if that's the case it's a cool thing."
Manuel remains sidelined after undergoing a minor procedure on his left knee last week. Marrone said that while he hopes the 16th overall pick will be ready to play in Week 1, the team will make preparations for Tuel to start.
"[Manuel's] working back so he's actually starting to move around now, which is a good sign," Marrone said, according to the team's website. "Then it's just a matter of how he heals and then when he's back he'll be our quarterback."
The Bills are proceeding as though Kolb's concussion, which was termed "serious," could be career-ending, a league source told ESPN.
Kolb will undergo a battery of tests, and the Bills do not want to rush him back even if he can continue his career, the source said.
ESPN NFL Insider Adam Schefter contributed to this report.