An elderly man has lost a key battle in his fight to stave off deportation for lying to Canadian immigration authorities about his Second World War activities with a Nazi death squad.

In a ruling this week, a Federal Court judge lifted a stay on his earlier decision that the government had been reasonable in stripping citizenship from Helmut Oberlander. In addition, Judge Michael Phelan sharply limited any possibility that Oberlander, 94, could take the case to the Federal Court of Appeal.

Phelan said he was mindful his decision "determines rights of appeal."

One of Oberlander's lawyers said on Thursday that next steps were uncertain.

"We don't have instructions at the moment about what he's going to do," Barb Jackman said.

The Ukraine-born Oberlander, who came to Canada in 1954 and became a citizen six years later, has steadfastly maintained he was just 17 when he was forced on pain of execution to join the Nazi death squad Einsatzkommando 10a, known as Ek 10a. The squad was responsible for killing close to 100,000 people, mostly Jewish.

In June 2017, the government revoked the retired businessman's citizenship for the fourth time since the mid-1990s, prompting his current effort to stave off deportation.

However, Phelan ruled in September that said it was reasonable Oberlander, of Waterloo, Ont., lose his Canadian citizenship for misrepresenting his war-time activities even though no evidence existed that he took part in any atrocities.

"It is uncontested that Oberlander obtained his Canadian citizenship by false representation or by knowingly concealing material circumstances by failing to disclose involvement in the SS at the time of his immigration screening," Phelan wrote. "There is no doubt that to have done so would have resulted in the rejection of his citizenship application."

To allow Oberlander to appeal the merits of the decision itself, Phelan was required under immigration law to "certify a serious question of general importance." Among the nine questions Oberlander's lawyers put forward were ones related to procedural fairness and even which members of cabinet made the decision to strip their client of his citizenship.

Phelan, who had stayed his ruling, on Wednesday rejected all Oberlander's arguments for certification, finding they did not "transcend the interests" of the immediate parties and raise issues of "broad significance or general application."

"The court cannot find a 'serious question of general importance' to be certified nor can it see how reformulation of any of the proposed questions would meet that threshold," Phelan said. "The stay is lifted and the court confirms that the judicial review is dismissed."

Should he choose to do so, Oberlander may yet be able to persuade the Federal Court of Appeal to hear the case on grounds outside of the Immigration Act. He does face a steep battle in that the higher court generally hears only a fraction of cases decided by Federal Court.

Following Phelan's September ruling, Immigration Minister Ahmed Hussen said at the time that Canada should never be a "safe haven for war criminals and people who've been accused of crimes, who've committed crimes against humanity."