Navalny was poisoned in late August and fell ill during a flight in Russia.
He was later taken to Germany for treatment.
Several foreign laboratories have determined that Navalny was poisoned with the neurotoxin Novitjok, which developed in the Soviet Union.
During his time abroad, the opposition politician has continued to be a nail in the eye of the Kremlin.
Among other things, he has, together with various media, managed to call an agent at the Russian security service FSB who told about the poisoning of him.
Russian investigators now say they suspect that Navalny has spent 356 million donated rubles (just over 39 million kronor) on the purchase of "personal property, tangible assets and to pay expenses (including for holidays abroad)".
"Stolen" donations
Therefore, from a legal perspective, the donations are to be regarded as "stolen", the committee of inquiry states in a statement.
Navalny himself wrote on Twitter that the new allegations against him are fabricated and look like a hysterical measure ordered by President Vladimir Putin.
He also writes that he foresaw that the authorities will try to imprison him when they have now failed to murder him.
Russian authorities, who officially deny any involvement in Navalny's illness on the plane, have already used a long list of lawsuits against him in the past.
Arrive in Moscow
On Monday, the federal prison authority FSIN demanded that Navalny leave Germany immediately and no later than Tuesday morning show up at their office in Moscow.
If this does not happen, he can be said to have violated the rules for a conditional release from a previous prison sentence, according to the authority.
Therefore, Navalny, whose suspended sentence expires on Wednesday, is also at risk of being thrown into prison again on the day he returns to Russia, according to FSIN.
Navalny and most observers say the lawsuits are politically motivated and run by the Kremlin.