Washington(CNN) Arizona Gov. Doug Ducey is expected to make an announcement as early as this weekend on who will replace Sen. Jon Kyl, sources familiar with the conversations in Arizona told CNN.

Ducey's office announced Friday that Kyl plans to step down from the US Senate at the end of this year, a few months after being appointed to fill the late Sen. John McCain's seat.

According to sources, the Republican governor's likely choice is GOP Rep. Martha McSally, who lost her bid for Arizona's other Senate seat during the 2018 election.

Whoever Ducey picks as a replacement will be able to serve until 2020, when there will be a special election to fill the remaining two years of McCain's term.

Before Kyl's decision was announced Friday, Senate Majority Leader Mitch McConnell had been leveraging his political power to try to convince Ducey to choose McSally, several Republican sources told CNN last month.

In Friday's announcement, the governor's office said a replacement to the seat will be announced in the near future. Arizona law requires Ducey, a Republican who was reelected to a second term, to pick an appointee that is the "same political party as the person vacating the office."

In September, Ducey tapped Kyl to temporarily replace McCain, who died in August -- just two years into his sixth Senate term. At the time, Kyl committed to serving through at least this year and said from the start that he would not run for re-election in 2020.

Kyl wrote in a letter Wednesday to Gov. Ducey saying that he will resign from the US Senate effective December 31, 2018.

"When I accepted your appointment, I agreed to complete the work of the 115th Congress and reevaluate continuing to serve," Kyl wrote in his letter to Ducey, released by the governor's office Friday. "I have concluded that it would be best if I resign so that your new appointee can begin the new term with all other Senators in January 2019 and can serve a full two (potentially four) years."

"Arizona needed someone who could hit the ground running from day one and represent our state with experience and confidence -- and that's exactly what Senator Kyl has done," Ducey wrote in a statement released Friday.

Kyl was elected to the US House in 1986 and the US Senate in 1994. He retired from the Senate in 2012 rather than seek re-election and went on to work as a lobbyist at the law firm Covington & Burling.

"Senator Kyl didn't need to return to the Senate," Ducey said in the statement. "His legacy as one of Arizona's most influential and important political figures was already without question. But he did return, and I remain deeply grateful for his willingness to step up and serve again when Arizona needed him. I wish him and his family all the best."

Kyl also praised McSally in November, who once worked on his staff as a national security adviser, when asked by CNN about her as a potential replacement should he resign.

"Martha McSally would be a very good member of the United States Senate, however she got there," Kyl said then, adding, "I can't think of anybody more qualified than Martha McSally."