Gardenhire announced his cancer diagnosis on Tuesday, via the team's official Twitter account.
"I'm going to fight it and deal with it," Gardenhire said in a statement. "It's a bump in the road and it's not how I envisioned starting Spring Training with a brand new team but it's part of life. With the backing of this ball club, we'll get through it and I'll get through it."
Diamondbacks manager Torey Lovullo also addressed Gardenhire's illness in the same release.
"We are a family," he said. "As a family, there's a series of tests that are going to come upon us and this is a big one, but we're going to come together and help Gardy through this to the best of our ability. We're not going to miss a step because we're committed to him."
Gardnhire joined Lovullo's staff in November after he sat out the 2015 and 2016 seasons. The 59-year-old previously spent 13 seasons as manager of the Minnesota Twins.
From 2002-14, Gardenhire led the Twins to six American League Central titles and an appearance in the 2002 American League Championship Series. He had a career record of 1,068-1,039 with the franchise.