In the absence of that, he warned that Russia's air campaign against Syria would only lead to further bloodshed for the war-torn country and bog down Moscow.
Russia, he predicted during a White House press conference, would get stuck in a "quagmire," adding, "It just won't work, and they're going to stay there for a while."
Saying Syria's civil war doesn't directly involve the United States -- but instead pits Assad's forces against rebel groups -- Obama admitted elements of his strategy had failed. A plan to train and equip opposition forces, which resulted in only a handful of trainees, "did not work the way it was supposed to," Obama said.
But asked whether he now backs no-fly zones in Syria -- which his former secretary of state, Hillary Clinton, recommended this week during her presidential campaign -- he warned against "easy, low-cost answers" to ending the war.
Asked to respond directly to her suggestion, he said that one's perspective changes when president.
"I think Hillary Clinton would be the first to say that when you're sitting in the seat that I'm sitting in in the situation room, things look a little bit different. Because she's been right there next to me," he said.
He also said, "I also think there's a difference between running for president and being president."
Instead, Obama insisted that the only solution was diplomatic, raising the possibility of a brokered deal to remove Assad from power.
Obama's comments come after a scramble by his administration to respond to Russia's strikes, which began two days after the President met Putin at the United Nations.
Obama's aides emerged from that meeting confident Putin was committed to defeating ISIS in Syria. But after the airstrikes began, the U.S. said Russian planes were instead targeting areas held by rebel forces opposed to Assad rather than ISIS terrorists.
Obama said Friday he didn't think anyone was "fooled" by Putin's strategy in Syria, which he said amounted to supporting Russia's sole "client state in the Middle East."
He said that during his meeting with Putin, he underscored the importance of transitioning Assad from power.
In a joint statement Friday, the governments of nations fighting ISIS -- including the United States, the United Kingdom and Saudi Arabia -- said Russia's military strikes "constitute a further escalation and will only fuel more extremism and radicalization."
The joint statement, using another acronym for ISIS, called on Russia to "to immediately cease its attacks on the Syrian opposition and civilians and to focus its efforts on fighting ISIL."
But Putin has showed little sign he's ready to end his military campaign in Syria. Russia is one of Assad's last remaining global backers, and the White House says Putin is looking to prop up Assad's regime as it appears to falter.
Russia's final remaining military base outside the former Soviet Union in positioned on Syria's coast, lending further urgency to Putin's desire to bolster Assad.