Bruins general manager Peter Chiarelli and his staff are determined to make sure no one arrives at the opening of training camp Friday thinking he’s guaranteed an NHL job.

Today, according to numerous news reports, the club invited veteran tough guy Brian McGrattan to camp on a tryout basis. So you can scratch Shawn Thornton off the short list of players lacking competition for their position.

In just 34 games last season, the 6-foot-4, 235-pound McGrattan managed to rack up 86 penalty minutes and 14 fights with Calgary. In 2005-06 and 2006-07 with Ottawa, the now-29-year-old McGrattan exceeded 100 penalty minutes, including this bout with Thornton in Nov. 2007.

Prior to joining Calgary last season, McGrattan struggled through the 2008-09 season with Phoenix, first entering the league’s substance abuse program and then injuring his shoulder.

Whether there’ll be an actual physical confrontation in this season’s training camp remains to be seen. However, before today the Bruins only had Jeremy Reich as a player that could be classified as a Thornton-like bruiser, and he (like Thornton) is a bit undersized. Now, just like the under-performing veteran forwards who’ll be pushed by some youngsters and Tuukka Rask being pushed by Tim Thomas in goal, Thornton knows exactly where the challenge to his existence on Boston’s roster is going to come from.