Rep. Jeff Flake (R) is expected to announce Monday morning that he will run for the seat of retiring Sen. Jon Kyl (R-Ariz.), a Republican strategist based in Arizona told Roll Call on Sunday.

The Senate Minority Whip revealed Thursday that he will not seek re-election to a fourth term in 2012.

When Flake was asked about his intentions Thursday, the six-term House Member told Roll Call, “This is Kyl’s day, but we’ll have an announcement soon enough.” He has been expected to jump into the race.

Roll Call Politics has rated the open-seat race as Leans Republican. Arizona is gaining a seat in reapportionment, and Democrats believe population gains could give them a boost.