Prime Minister Stephen Harper says he worries about violence and injuries in professional hockey, and that the NHL has to do something about it.

Harper — whose book on the early days of professional hockey and the Toronto Maple Leafs,  A Great Game, hits store shelves Tuesday — said the game has always been physical.

"I think it's played as well today as it's ever been played. I do worry with the speed, the size of the players, the new equipment, I do worry about not just the violence but the very serious injuries that we're seeing and I do think the NHL has to address that problem," Harper said in an interview with Fan 590.

The PM said hockey has always been violent, and in the time period he researched, players were "clobbering each other with sticks while they were wearing virtually no equipment."

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Stephen Harper's hockey history book is to be released Tuesday. (AGreatGameBook.com)

Harper's book is about the early days of professional hockey at the start of the 20th century.

"I'm torn on that [eliminating fighting]," he said.

"I don't watch hockey for the fights. It wouldn't bother me if we had no fights ... I don't like fighting as a strategy, I actually hate it as a strategy, but I think the fact that it happens once in a while in a tough sport is not a surprise."

The NHL season is barely a month old but has already seen several lengthy suspensions and serious injuries from in-game fights. 

In a game to open the season, Montreal tough guy George Parros suffered a concussion after he fell to the ice during a fight with the Toronto Maple Leafs' Colton Orr.

Last week, during the Philadelphia Flyers' embarrassing rout at the hands of the Washington Capitals, Philadelphia's goaltender skated the length of the ice to challenge his Washington counterpart and landed several hard punches. Neither fight resulted in a suspension.

Proceeds from Harper's book go to a fund to support military families.