The Indianapolis Colts and veteran quarterback Joe Flacco have reached agreement on a one-year deal worth up to $8.7 million, sources told ESPN's Adam Schefter on Wednesday.

Flacco, who played for the Cleveland Browns last season and won NFL Comeback Player of the Year honors, will receive $4.5 million guaranteed in the deal, according to sources.

In Indianapolis, Flacco will back up and mentor second-year quarterback Anthony Richardson. Flacco also will provide some peace of mind for the Colts after Richardson missed 12 games as a rookie following a season-ending shoulder injury and one game earlier in the campaign because of a concussion.

Flacco gives the Colts a reliable backup who won't take practice reps from a young quarterback still in his developmental stage. And the 17th-year signal-caller can mentor Richardson, who started just one full season at Florida and lost out on precious opportunities to play during his rookie campaign.

With Gardner Minshew, last year's backup QB in Indy, signing with the Las Vegas Raiders this week, the Colts get a proven replacement in Flacco. Flacco's arm strength should also be a boost over Minshew, who often was reluctant to throw the deep ball. That is something Colts coach Shane Steichen admitted was missing from the Colts' offense last season. In Richardson and Flacco, the Colts now have two of the biggest arms in the NFL.

Flacco signed with the Browns' practice squad in November after a season-ending shoulder injury to starting quarterback Deshaun Watson. Two weeks later, Flacco made his first start. He went on to become the first quarterback in NFL history to throw for over 250 yards and multiple touchdowns in his first five games with a new team.

Flacco also propelled the Browns to a four-game winning streak and the No. 5 seed in the AFC playoffs. He finished the regular season with 1,616 yards passing, 13 touchdowns and eight interceptions in five games.

Cleveland, however, fell in the first round of the postseason to the Houston Texans. Flacco threw pick-sixes on back-to-back possessions in the second half of the 45-14 defeat.

Flacco, 39, won the Super Bowl with the Baltimore Ravens in 2013 and was named Super Bowl MVP. He has thrown for 43,936 yards and 245 touchdowns in a career that also includes time with the Denver Broncos, New York Jets and Philadelphia Eagles.

ESPN's Jake Trotter and Stephen Holder contributed to this report.