The veterans had to clear waivers and did so as the Hawks were on the ice for practice.
Regin had four points in 17 regular-season games with the Hawks last season and appeared in five postseason games.
Leighton was signed as a free agent during the summer with the intent of providing depth at goaltending and starting in Rockford.
The Hawks also placed T.J. Brennan, acquired in the Nick Leddy trade Saturday, on waivers according to TVA Sports.
Here were the forwards line during practice: Sharp-Toews-Hossa; Bickell-Richards-Versteeg; Saad-Shaw-Kane; Smith-Kruger-Morin.