The draft pick will be a conditional fourth-round pick in 2016 or a third-rounder in 2017.
Gagner had 15 goals and 26 assists in 81 games after being traded to Arizona from Tampa Bay before last season.
Grossman had five goals and nine assists in 68 games with the Flyers last season. The Swedish player has 10 goals and 69 assists in 531 career NHL games with Philadelphia and Dallas.
A former winner of the Hart and Norris trophies, Pronger has not played since 2011-12, when he appeared in 13 games with the Flyers.
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