Diaz has six goals and 39 assists along with 52 penalty minutes through 145 games in the National Hockey League. He has also played nine NHL playoff games.
The 28-year-old had two goals and 13 assists in 63 games with three teams — the Montreal Canadiens, Vancouver Canucks and New York Rangers — last season.
The Flames also announced Monday that they had assigned defenceman Tyler Wotherspoon to the Adirondack Flames of the American Hockey League.
Wotherspoon, 21, had four assists and four penalty minutes in 14 games with Calgary last year.