Detroit will retain 50% of Panik's salary.
Panik has 88 goals and 106 assists in 517 regular-season games in nine seasons with Tampa Bay, Toronto, Chicago, Arizona, Washington and Detroit. The 30-year-old Slovak split last season with Washington and Detroit, finishing with four goals and nine assists in 48 games.
Leddy, also 30, has 65 goals and 271 assists in 776 regular-season games in 11 seasons with Chicago and New York. He has seven goals and 26 assists in 121 playoff games, helping the Blackhawks win the 2013 Stanley Cup. Last season, the former University of Minnesota star had two goals and 20 assists in 56 games.