On Tuesday, Ducey refused to say what he would do if Kyl steps down after this year, beyond saying that he would not appoint himself.
Prolonging the uncertainty over who will fill the late John McCain's U.S. Senate seat, the governor of Arizona on Tuesday announced the appointment of former Sen. "Jon Kyl" and that he is "prepared to hit the ground running".
Kyl, 76, was to fly to Washington to be sworn in possibly just days before a high-stakes Senate vote on the confirmation of Brett Kavanaugh, President Donald Trump's pick to be the next US Supreme Court justice.
When Kyl joins the Senate, Republicans will restore their 51-to-49 advantage over Democrats for the first time this year. Kyl's appointment will make it possible for him to vote for the nomination.
Widow Cindy McCain said it was a "great tribute" to her late husband that their close friend Kyl will return to public service by assuming McCain's seat.
Kyl, 76, served alongside McCain in the Senate for almost two decades and rose to the No. 2 position of Senate Republican whip. Jon Kyl but said he has only committed to serve until the end of the year.
Kyl, an experienced foreign policy hand, will be entering a narrowly divided Senate where Republicans could gain or lose seats in November. In that cycle, voters will get to decide who fills the remainder of McCain's seat through 2022.
The GOP is hoping Kyl will be a more reliable partisan vote than McCain, whose opposition to a partial repeal of President Obama's health care law pitched the party into turmoil past year.
Kyl is well-respected in Arizona and has been able to avoid numerous battles with activists that complicated McCain's career and that of the state's other senator, Jeff Flake, who is retiring because his feud with Trump made his re-election impossible.
McCain's fellow Arizonan, retiring U.S. Senator Jeff Flake, who has been one of Trump's most prominent Republican critics, praised the pick on Twitter, calling it "an excellent choice!"
Ducey said Kyl would serve through at least the end of the year and expressed hope he would stay in the seat longer. "I don't really have a relationship with President Trump".
U.S. Senator John McCain (R-AZ) speaks after being awarded the 2017 Liberty Medal by former U.S. Vice President Joe Biden (unseen) at the Independence Hall in Philadelphia, Pennsylvania, U.S., October 16, 2017.
Kyl has worked closely with Kavanaugh, helping him navigate and prepare for meetings with senators leading up to his confirmation hearing this week.
The appointment brings a more conservative bent to the Senate given Kyle's voting record and how it veers from that of McCain, a maverick who sometimes collaborated with Democrats on major legislation.
But Kyl has also at times been unreserved in his criticism of Trump.
The race pits Republican Rep. Martha McSally against Democratic Rep. Kyrsten Sinema.