Matthias was a late round pick in the 2004 OHL Priority Draft, as such it was surprising that he made the Belleville Bulls as an under-aged player. Used to being a top star with his Minor Midgets team (he had a 31-goal season with the Mississauga Senators Minor Midgets in 2003-04), in his freshman OHL season the big center only tallied two points (one goal) in 37 games.
2005-06: After a slow start, Matthias progressed as this season went along. With 34 points in 67 games, and a seven game scoring streak in January, Belleville counted on Matthias more and more as the season wore on. He played for Canada in the Under-18 World Junior Championships in Sweden, where he scored one goal in seven games. However, Matthias played his best hockey all season in the playoffs for the Bulls, leading the team with three goals in their first round series which was lost against the Brampton Battalion.
Matthias is used to being overlooked and then working hard to shine. As the 2005-06 season went along, he looked like he was getting more and more comfortable in an offensive role for the Bulls.
Drafted 2nd round (47th overall) 2006 Entry Draft by Detroit
2006-07: Matthias more than doubled his offensive production with the Bulls, totaling 73 points (38 goals, 35 assists) in 64 games, along with 61 penalty minutes and a +11. He participated in the 2006 ADT Canada/Russia Challenge, playing on the OHL team. He was dealt to the Florida Panthers in February 2007.
2007-08: Matthias was on a point-per-game pace for the better portion of this season, as his Belleville Bulls took the top spot in their conference. He finished with 32 goals and 47 assists for a total of 79 points even as he was in and out of the lineup while facing a variety of health issues.