Russian opposition leader Aleksei Navalny was summoned by police one day after his release following 50 days in jail, and the vocal Kremlin foe could face a new criminal charge.

Navalny wrote on Twitter that he reported to a police station in Moscow on October 15 after investigators informed his lawyer that he would be charged with libel in a case dating back to 2016.

Navalny said that he and his lawyer spent about three minutes at the police station, where he was presented with a pending charge against him but was not charged.

Navalny said earlier in the day in his video blog that the possible libel charge related to a case initiated two years ago by Pavel Karpov, a former police investigator.

In a report published online in 2016, Navalny's investigative organization accused Karpov of involvement in the death of Sergei Magnitsky, a lawyer who in 2007 revealed what he said was a massive scheme whose perpetrators defrauded the state of $230 million.

Magnitsky, who was imprisoned and accused of the same alleged crimes he helped discover, died in a Moscow jail in 2009 after being denied medical care and treated in a way that rights activists said amounted to torture.

Magnitsky's death led to a 2012 U.S. law known as the Magnitsky Act, which imposed sanctions on many Russian officials and law enforcement officers, including Karpov, infuriating the Kremlin.

If charged and convicted, Navalny could face a fine of up to 480 hours of community work, but no jail time or prison sentence.

The police summons came a day after he walked free after spending 50 days in jail on administrative charges related to antigovernment protests he has organized.