The slander case is focused on Navalny's comments about a video, in which World War II veteran Ignat Artemenko spoke in support of constitutional amendments.
"[He is] a defendant over insulting a veteran ... at the very least, it is unacceptable to insult veterans in our country," Peskov told reporters.
Alexei Navalny will deliver his final statement in the World War II veteran slander case on 20 February, a Sputnik correspondent reported from the courtroom.
"The hearing is postponed to February 20, 14:00 [Moscow time, 11:00 GMT]," judge Vera Akimova said.
The hearing will start with Navalny's statement.
The criminal case was launched over Navalny's strong-worded comments on a video, in which the veteran spoke in favor of constitutional amendments. The prosecution asked a district court in Moscow on Tuesday to fine Navalny 950,000 rubles ($12,942) and to uphold the 3.5 year sentence in the Yves Rocher fraud case.
Navalny can face fines or compulsory labor under the defamation case. Although Russian President Vladimir Putin signed late last year a law introducing prison sentences for online defamation, this is not applicable to cases that were initiated earlier.