O'Brien was invited to Panthers' camp on a professional tryout basis, Harvey Fialkov of the South Florida Sun-Sentinel reports. With the Panthers searching for some veteran defensive depth to complement youngsters Aaron Ekblad, Erik Gudbranson and Dylan Olsen, O'Brien could provide exactly what the club is looking for. O'Brien hasn't shown much offensive ability during his time in the NHL, but does offer some physicality and has previously ranked among the blueliner leaders in penalty minutes. If he makes the club, O'Brien would likely slot in on the third pairing, or as a seventh defenseman.