The Florida Panthers defensive corps is full of offensive-minded defensemen. And it could be locking up another with a reported contract extension. Sportsnet reported Saturday night that the Panthers were working on an eight-year contract extension with Mike Matheson with an average annual value of about $5 million. Matheson was one of the Panthers’ most-used players last season, averaging 21:03 of ice time as he played in 81 games. He had seven goals and had 10 assists in his first full season in the NHL Matheson was a first-round pick in the 2013 draft and was scheduled to be a restricted free agent next season. The 23-year-old Boston College product would join Ekblad as young Panthers defensemen to sign long extensions. Aaron Ekblad, 21, just started the first season of his eight-year, $60 million extension. Keith Yandle led the team with 36 assists last season. Ekblad has scored double-digit goals in each of his three seasons. Matheson is built more in Yandle and Ekblad’s mold than a shutdown defenseman like Alex Petrovic. But that doesn’t mean Petrovic can’t chip in on offense. During the season-opening 5-3 loss to Tampa Bay on Friday, two Panthers defensemen crashed the net, leading to two Florida goals. In the second period, Petrovic slung a pass from just to the left of the Lightning net, setting up an easy goal by Connor Brickley. Later in the period, defenseman Mark Pysyk finished in front of the net with a backhand goal.