"Before making a decision on an extension, we will need to give an overall assessment of the effectiveness of the deal," President Vladimir Putin's spokesman Dmitry Peskov told reporters.
Last week Russia quit the deal, which expires November 19, for four days over a drone attack on its Black Sea Fleet in Crimea.
Moscow resumed its participation in the agreement on Wednesday, after saying it had received security guarantees from Ukraine on demilitarising a maritime corridor.
Meanwhile "The Black Sea Grain Initiative is making a difference!" United Nation chief Antonio Guterres told journalists.
"As of today, ten million metric tons of grain and other foodstuffs have been shipped through the Black Sea corridor. It has taken just three months to reach this milestone."
But Peskov said Moscow's return "does not mean" it would necessarily decide to extend the deal later this month.
He said Russia only trusted Ukraine's guarantees because they were brokered by Turkey, praising Ankara's role in securing them.
On Wednesday, Putin threatened to leave the deal again if Kyiv violated its guarantees.
Deputy Foreign Minister Andrei Rudenko said the same day that Moscow's return to the deal was a "separate issue" from its potential extension.
He added that Moscow had concerns over the way the deal was being implemented.
Meanwhile, six grain ships left Ukraine's ports on Thursday, a day after Russia rejoined a deal to allow exports through the Black Sea, Turkey's defense minister said.
"After the resumption of the grain initiative, six ships left Ukrainian ports," Defense Minister Hulusi Akar was quoted as saying by the official Anadolu news agency.
Russia is also pushing for having restrictions lifted on its own sales of grain and fertilizer.