During an interview for NBC's "Today Show," the president said that what Weiner did in exchanging sexual messages over the Internet with several women was "highly inappropriate" and that Weiner had embarrassed himself, his wife and his family.
The president didn't explicitly call for Weiner to resign but said that when a politician gets to the point where he can't serve as effectively as needed, in his words, "then you should probably step back."
Weiner is on a temporary leave of absence, seeking treatment at an undisclosed location.
The embattled congressman has admitted to exchanging messages and photos that ranged from sexually suggestive to explicit, with several women online.
New photos of Weiner emerged over the weekend on the gossip website TMZ, leading to more calls for his resignation. The photos were more lewd than the ones previously released from Weiner's Twitter and email accounts.
The photos were reportedly taken in the gym reserved for members of Congress, and they show Weiner almost completely nude. The photo appeared to be shot with Weiner's Blackberry while he posed in front of a mirror.
Rep. Steny Hoyer of Maryland, the No. 2 House Democrat, said Sunday it would be "extraordinarily difficult" for Weiner to be effective in Congress, while House Democratic leader Nancy Pelosi of California and Rep. Debbie Wasserman Schultz, the national party head, have both said Weiner must go.
"We have made clear that he needs to resign, he needs to focus on getting his own personal issues in order," Wasserman said.
Hoyer said the ethics committee process to decide whether Weiner had committed an expellable offense would take time and "I really don't know if we have that time."
The Associated Press contributed to this report.