"Ultimatums do not help anyone move forward. But if no explanations follow from Russia in the coming days, we will have to discuss the response with our partners", Maas told Germany's Bild am Sonntag newspaper on Sunday.
Asked whether he thought the Russian government could be behind Navalny's alleged poisoning, the German foreign minister said "there were many indications of that", adding that "Russia is currently faced with a challenge" for that reason.
"We have high hopes for the Russian government to solve this serious crime. If [the Russian government] has nothing to do with the attack, then it is in his own interest to prove it with facts", Maas added.
Heiko Maas also said that Germany hopes Russia's response to the issue will not prompt Berlin to alter its stance on the Nord Stream 2 gas pipeline project.
"I hope that the Russians will not make us change our position on Nord Stream 2. Those who demand it must perceive the consequences. The Nord Stream 2 project includes more than 100 companies from 12 European countries, with around half of them from Germany", Maas said.
Echoing German Chancellor Angela Merkel's statement from last week, Maas said that "bringing the [Navalny case] debate down to only Nord Stream 2 was not consistent with what had happened".
Russia, too, has called for not linking Nord Stream 2, a commercial project, to the Navalny case, as stated by Kremlin spokesman Dmitry Peskov earlier this week.
Navalny is currently undergoing treatment in the Berlin-based Charite hospital after suffering a medical emergency in late August. On Wednesday, the German government said that doctors found traces of a nerve agent from the Novichok group in his system. This prompted many in the West to call for new economic sanctions against Russia.
On 20 August, Navalny fell ill during a domestic Russian flight. He was initially treated in the Siberian city of Omsk, where the plane made an emergency landing. Two days later, once the doctors established he was fit for cross-border aerial transportation, the opposition figure was flown to Charite for further treatment.
German doctors initially claimed they found traces of a substance from the group of cholinesterase inhibitors in his system, before flagging it as Novichok poisoning.