Coach Pete Carroll had said on Monday that the duo would split reps early in the week before a decision was made on who the starter would be for Saturday's game. Seattle does not have to submit an official practice participation report to the league until Wednesday.
Whitehurst started and helped lead Seattle to a 16-6 win over St. Louis last Sunday that wrapped up the NFC West title. Hasselbeck sat out that game with a hip strain suffered a week earlier against Tampa Bay.
Whoever is under center will have do without tight end Chris Baker and guard Chester Pitts on Saturday.
Seattle placed both on season-ending injured reserve Tuesday, but has not filled the spots on the active roster ahead of Saturday's NFC playoff game against New Orleans. Baker fractured a bone in his hip and Pitts suffered a serious concussion in last Sunday's 16-6 win over St. Louis.
Pitts started five games at left guard this season, but was replaced for the finale by Tyler Polumbus. Baker finished the year with nine receptions.
Seattle also placed Chris Henry on the practice squad injured reserve, released linebacker Vuna Tuihalamaka and signed running back Andre Anderson and tight end Nick Tow-Arnett to the practice squad.
Information from The Associated Press contributed to this report.