National Hockey League roundup

Ristolainen skated backward through the neutral zone on Tuesday and hit Guentzel hard in the head when he didn't have the puck. Guentzel initially tried to skate to the bench before falling to the ice. He eventually made his way off with help from a trainer but did not return and was diagnosed with a concussion.

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Toronto Maple Leafs defenseman Roman Polak was suspended for two games by the NHL for boarding Columbus Blue Jackets forward Oliver Bjorkstrand.

The incident occurred one minute into the third period of Toronto's 5-2 victory on Wednesday. Bjorkstrand did not return after the hit by Polak, who was assessed a major penalty and a game misconduct. The 30-year-old Polak will forfeit $25,000 under the terms of the Collective Bargaining Agreement.

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New York Islanders forward Ryan Strome will be sidelined for several weeks with a broken wrist, Newsday reported.

Strome sustained the injury late in the second period of Wednesday's 3-2 victory over the New York Rangers.

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Florida Panthers defenseman Aaron Ekblad has been ruled out Thursday against the Arizona Coyotes with a sore neck.

Ekblad missed four games with a concussion before returning for Tuesday's 4-3 loss to the Carolina Hurricanes. He has 10 goals and 11 assists in 68 games this season.

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The New York Islanders turned to a familiar face by recalling goaltender Jaroslav Halak from Bridgeport of the American Hockey League.

Halak, who has been with the Sound Tigers since early January, is rejoining the Islanders with the NHL club set to play three games in four days.

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The New York Rangers assigned goaltender Magnus Hellberg to Hartford of the American Hockey League.

Hellberg, 25, was recalled by the Rangers on an emergency basis last Thursday but did not play. He has appeared in one game with New York this season, stopping all four shots he faced against the Dallas Stars on Jan. 17.

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The Chicago Blackhawks agreed to terms on a two-year contract extension with forward Tanner Kero through the 2018-19 season.

Kero has five goals and seven assists in 38 games with the Blackhawks this season. He began the season with AHL Rockford, where he led the club with seven goals and 20 points before being recalled on Dec. 22.

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Goaltender Chris Nell signed with the New York Rangers.

The 22-year-old Nell appeared in 34 games for Bowling Green this season, posting a 17-14-2 record with a 2.15 goals-against average, a .916 save percentage. He also had four shutouts for the second straight season.