"The ban will make his work very complicated. Subsequently, it will be very easy to say that he (Zingeris) was biased, did not research and took no interest," he told BNS.
Zingeris was informed on Thursday that he had been barred from entering Russia for five years.
"My opinion about this yet another move, possibly a conscious one, is very negative," Linkevičius said.
Zingeris said at a news conference that the Kremlin's decision had derailed his plans to go to Moscow to collect material on the murder of Nemtsov and Russian authorities' investigation into the killing, adding that he would now have to do so remotely.
PACE in May 2017 appointed the Lithuanian lawmaker as a rapporteur in drafting a resolution on the assessment of the circumstances of the murder and the investigation of these circumstances.
Zingeris is a member of the Board of Trustees of the Boris Nemtsov Foundation for Freedom.
Nemtsov was shot dead on a bridge near the Kremlin on February 27, 2015.
Five men have been convicted in the assassination, but Nemtsov’s family and supporters believe the real masterminds of the murder have escaped justice.
Zingeris is not the only Lithuanian lawmaker slapped with a five-year entry ban into Russia.
The Russian Foreign Ministry said in April that it had imposed sanctions in response to Vilnius’ “Magnitsky list" of Russian nationals barred from entering Lithuania.