In the first breakthrough towards a possible peace deal in years, envoys from Moscow and Kiev agreed at talks on Tuesday (October 1) on an election schedule for the Donbass region and on legislation giving it special status.
Ukraine also agreed to call back its forces from the current contact line with separatist fighters.
But for many Ukrainians, these measures represent a huge betrayal by Zelenskiy, who took power in April after a landslide election win.
The war in eastern Ukraine has killed more than 13,000 people since April 2014.
Last week's deal opened the way for a resumption of top-level peace talks to end the conflict, which helped send Russia's ties with the West to post-Cold War lows in 2014.
Zelenskiy said last week that he would discuss a peace deal for Donbass in the upcoming four-way talks with Russia, Germany and France.
He said any elections in Donbass would be held only after all Russian troops had left.
Russia denies having troops there.
As things stand, Zelenskiy's "Servant of the People" party, which holds a majority of 251 seats in the Ukrainian parliament, is still short of the 300 votes needed to change the constitution and give autonomy to Donbass.