The person spoke Wednesday on condition of anonymity because the team had not yet made an announcement.
Ryan, who had a record seven no-hitters, won 324 games in 27 seasons, the last five with the Rangers.
The 61-year-old Ryan replaces Jeff Cogen, who owner Tom Hicks moved to the Dallas Stars during a shakeup of his hockey team in November.
Ryan leaves the Astros with more than a year remaining on a five-year personal services contract he signed in 2004. He most recently served as special assistant to the general manager, scouting players and holding pitching camps.
The agreement was first reported by the Fort Worth Star-Telegram.
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