"Damar remains in the ICU (intensive care unit) in critical condition with signs of improvement noted yesterday and overnight," the Bills said in a social media post.
"He is expected to remain under intensive care as his healthcare team continues to monitor and treat him."
During the first quarter of the Bills' penultimate regular season game against the host Cincinnati Bengals, Hamlin got to his feet after making a tackle and then collapsed.
After having his heartbeat restored on the field as stunned players from both teams cried, prayed and hugged, an ambulance took Hamlin to University of Cincinnati Medical Center.
U.S. President Joe Biden, speaking to reporters in Hebron, Kentucky on Wednesday, said Hamlin's collapse was not a sign that the NFL has become too dangerous, while noting the inherent risk of a sport with violent collisions on nearly every play.
"I think working like hell on the helmets and the concussion protocols, that all makes a lot of sense. But ... it is dangerous. We've got to just acknowledge it."
The Bills offered no further details, but Hamlin's friend and business partner Jordon Rooney said in an ESPN report earlier on Wednesday that doctors saw promising readings overnight that they had hoped to see by Wednesday morning.
Rooney did not immediately reply when asked by Reuters to provide details on Hamlin's condition.
Earlier, the Bills said they would hold meetings and a walkthrough - a slower-paced practice in which players typically do not wear pads and go through plays without physical contact - on Wednesday and that there would be no media availability.
The Bills' game against fellow Super Bowl contender the Bengals was postponed on Monday after Hamlin collapsed on the field.
The National Football League, whose regular season concludes on Sunday, has said the Buffalo-Cincinnati game would not resume this week.
During a conference call with reporters on Wednesday, NFL Executive Vice President of Communications Jeff Miller said the conversation about what to do about the game has started and a decision will be made in the coming days.
The game, if played, would have play-off implications for both teams as they are battling with the Kansas City Chiefs for the top seed in the American Football Conference, which comes with a first-round play-off bye.
The Bills are scheduled to host the New England Patriots on Sunday.