Cassel, 30, had been with the Chiefs for three seasons, signing with Kansas City after four years mostly as a backup to Tom Brady at New England.
The Chiefs this week traded draft picks to get Smith from the San Francisco 49ers and signed Daniel, who played collegiately at Missouri, as a free agent. Daniel has played just five games over four seasons with New Orleans.
Smith was the starter for the 49ers until he was hurt this past season and his replacement Colin Kaepernick took San Francisco to the Super Bowl.
With Smith and Daniel joining the Kansas City roster, it was expected that Cassel would be released.
There were reports after the Chiefs' roster move that Cassel had signed with the Minnesota Vikings. The St. Paul (Minn.) Pioneer Press said Cassel agreed to a multiyear deal with the Vikings and was penciled in as a backup to starter Christian Ponder.
Cassel was the starter for the Patriots in 2008, when Brady was injured in the first game of the season -- against Kansas City -- and missed the season. He was traded to the Chiefs the next February.
He played 48 games in Kansas City, starting 47, but his playing time was limited to seven games in each of the last two years by injuries.
While with Kansas City he completed 57.4 percent of his passes for 9,549 yards and 59 touchdowns against 44 interceptions. For his 78-game NFL career, he completed 1,203-of-2,044 passes for 13,495 yards and 82 touchdowns.