The Dolphins decided against drafting a quarterback, which leaves holdover David Fales and veteran newcomer Brock Osweiler to battle for the No. 2 job. Miami also claimed veteran Bryce Petty off waivers as further insurance last week.
Gase, speaking Thursday before the start of a rookie minicamp, said he'd be comfortable turning to Fales or Osweiler this season if Tannehill were sidelined by an injury.
"If I wasn't, we'd have somebody else here," Gase said.
Bringing in an emergency replacement wouldn't be necessary, Gase said. Last year he coaxed Jay Cutler out of retirement after Tannehill suffered a knee injury that forced him to miss the entire season.
"There's a lot of confidence as far as the guys we have," Gase said.
Osweiler signed a one-year contract in March after going 0-4 as the Denver Broncos' starter last season. Gase was an assistant with the Broncos when Osweiler was a young reserve for them in 2012-14.
Gase said a conversation with Osweiler convinced him a reunion would be wise.
"Just hearing him and where he was mentally and what he wanted to accomplish and how he wanted to get his career rolling again ... everybody in the building liked him, and I felt good about it," Gase said.
Fales had only two career completions before getting an extended tryout in the Dolphins' 2017 finale against Buffalo, when he went 29 for 42 for 265 yards with one score and one interception.
"I was impressed with some of the things he did in that game," Gase said. "Sometimes he makes plays and you're not really sure how he did it."
Matt Moore wasn't re-signed this offseason after seven years as the backup quarterback. The importance of the job is magnified because Tannehill has suffered two serious left injuries in the past 18 months, but he has been working out and cleared for offseason practices.
"I see a guy who is very confident," Gase said. "He's really smooth with what we're doing in throwing sessions. He looks good to me."
The Dolphins went 6-10 last season and then parted with three players with Pro Bowl resumes: defensive tackle Ndamukong Suh , center Mike Pouncey and receiver Jarvis Landry. There were financial reasons, and Gase also wanted a change in culture on a team that was undisciplined and wildly inconsistent in 2017.
"You look at how the group gets along," Gase said. "How do they work together? Do they push each other? Are they all pulling the same direction? Do you have guys who are going to quit on you or push forward when things get hard?
"The way we're assembled right now, I like our makeup."