PITTSBURGH -- After an initial 53-man roster that was short on cornerbacks, the Steelers have fortified the position by acquiring Ahkello Witherspoon in a trade with the Seahawks for a 2023 fifth-round pick, the teams announced.

Witherspoon, 26, signed a one-year, $4 million deal with the Seahawks in March and was expected to compete for the starting job at left cornerback, but Seattle moved D.J. Reed over to the left side and Tre Flowers into the starting role at right cornerback, making Witherspoon a trade candidate. A day earlier, Seattle traded a 2022 sixth-round pick to the Jacksonville Jaguars for Sidney Jones.

Witherspoon was frustrated by being relegated to a backup role, a source told ESPN's Brady Henderson.

The Steelers will take on $1.5 million of Witherspoon's salary, while the Seahawks save that amount against their cap. However, Seattle is still on the hook for $1.25 million in dead money in 2021 and 2022 from his signing bonus.

Witherspoon was taken in the third round by San Francisco in 2017 and started 33 of 47 career games with the 49ers in four seasons. He recorded 116 tackles and four interceptions and had 24 passes defended.

The Steelers initially had just four cornerbacks on the 53-man roster following cuts: Cam Sutton, James Pierre, Justin Layne and Joe Haden. They added one more a day later, signing Arthur Maulet after moving three other players to injured reserve. Before adding Maulet, defensive coordinator Keith Butler expressed apprehension about entering the season with so few cornerbacks.

"I don't think anybody's comfortable with four cornerbacks," Butler said. "We've got guys who can play different positions. Cam can play different positions. He can play the nickel. Forty-two [Pierre] has shown that he can play in preseason.

"We think we're OK right now to play them in different positions. If somebody becomes available out there in never-never land, we'll see what happens."

Witherspoon gives the Steelers depth at cornerback behind veterans Haden and Sutton, who emerged late in training camp as the likely slot cornerback after Mike Hilton's departure. With Sutton in the slot, undrafted free agent Pierre was slated to be the outside cornerback opposite Haden. The outside cornerback depth is young and relatively unproven, and Witherspoon's experience elevates the position group.

The Steelers released defensive lineman Henry Mondeaux to make room on the roster for Witherspoon.