AfD spokesman Jörg Meuthen tweeted a gruesome photograph of an unconscious Magnitz with a large, bloody gash on his forehead and a severely swollen right eye.
Magnitz was beaten over the head with an unidentified object by at least three men wearing dark clothing and hoods or hats, who then fled, police said. Authorities have said they have little doubt the assault was politically motivated.
"This is the result of the ostracism and agitation AfD faces", he said, suggesting other German political parties were partly responsible for the attack because they had compared AfD to Adolf Hitler's Nazi party because of its nationalist rhetoric and campaigns against migrants. Shortly after he left a local newspaper's New Year's reception, the perpetrators knocked the 66-year-old down with a wooden plank and continued kicking his head until a construction worker, who happened to be nearby, intervened.
AfD views the country's established political parties with contempt.More news: Kim Jong Un departs Beijing after meetings with Xi Jinping
Police have been stationed outside Magnitz's hospital room to protect him against further attacks and to interview him as soon as he is able to speak with officers, The Guardian explained.
Leading politicians across the political spectrum in Germany condemned the attack Tuesday.
Foreign Minister Heiko Maas, a centre-left politician who has been a strong critic of AfD, tweeted that "violence must never be a means of political confrontation - no matter against whom or what the motives are". "Whoever carries out such a crime has to be punished accordingly".
Picture taken on October 5, 2017 shows Frank Magnitz, politician of the anti-immigration populist party Alternative for Germany (AfD), posing at the Bundestag (lower house of parliament) in Berlin.More news: Bayern Confirm They Want To Sign Chelsea Attacker
Frank Magnitz was brutally beaten, his party said.
Last week, an AfD office in the eastern town of Döbeln was damaged by an explosive device, though no one was injured. Saxony holds a state election in September.
"Today is a black day for democracy in Germany", the AfD said, noting that Magnitz remains in serious condition.
Bremen police said they believe the attack on Frank Magnitz, an MP in Germany's national parliament who leads Alternative for Germany's (AfD) local branch, was a "politically motivated act, given the victim's work".More news: Former Miami Dolphins coach Adam Gase takes over at New York Jets