Schroder said the Hawks must snap their seven-game losing streak with their current limited roster, which will be without the three starters for at least one more game.
"I'm saying now we have to change something," Schroder said Monday. "We can't wait until they come back. Maybe it's too late then."
The Hawks announced Monday night that Millsap, a four-time All-Star who has missed the last five games, will miss three more games after being diagnosed with left knee synovitis. The diagnosis of the condition, the inflammation of a membrane in the knee joint, came after Millsap was examined by Dr. James Andrews in Pensacola, Florida, and by two Atlanta specialists.
The team said Millsap had a non-surgical procedure at Atlanta's Emory Hospital, and his status will be updated "as appropriate."
The Hawks are in a three-way tie for fifth place in the Eastern Conference. They are only two games ahead of eighth-place Miami, which currently holds the final playoff spot, and 2+ ahead of ninth-place Chicago.
The Hawks see they could drop out of the playoffs if they don't quickly end the losing streak.
"The NBA isn't easy," Schroder said. "You've got to win games to make it in the playoffs."
Coach Mike Budenholzer said the other two injured starters also will not play in Tuesday night's home game against Phoenix.
Bazemore, who has missed four straight games with a right knee bone bruise, said he hopes to return for Wednesday's game at Philadelphia.
Sefolosha, held out against the Nets with a right groin strain, was seen working on an elliptical machine at the portion of Monday's practice open to media. There is no timetable on Millsap's return.
Before the losing streak, which matches the team's longest of the season, the Hawks were competing with Toronto for the fourth seed in the East and home-court advantage in the first round of the playoffs.
Home-court advantage is now a distant dream.
Atlanta is tied with Milwaukee and Indiana for fifth following Sunday's 107-92 loss to New Jersey, which owns the NBA's worst record.
The latest ugly loss left Atlanta in what Bazemore described as "a dark time." Even so, he insists the players' spirit is not broken.
Bazemore pointed to players taking extra shots after practice and said, "My teammates are still laughing. ... We're still alive and kicking."
Budenholzer's message is for players to avoid trying to do too much to fill the void left by the injured starters.
"I think to some degree we're all pressing," Budenholzer said. "Coaches pressing, each guy individually. It comes from actually a good place. They want to win. They want to have success and it's just remembering that the best way for us to have success is to do it as a group and do it together."
Budenholzer said rookie Taurean Price, who had 17 points, six rebounds and three steals in his first start against the Nets, likely will remain in the lineup against Phoenix.
Ersan Ilyasova and Tim Hardaway Jr. combined to shoot only 8 of 30 against the Nets. Atlanta's depleted bench was outscored 46-7 by Brooklyn's backups.
Budenholzer said Bazemore is "very close" to playing and could be cleared after "another good day."
Bazemore said he has done "pretty much everything" on the court in testing his knee, including change-of-direction drills.
"I'm starting to feel good," Bazemore said. "Things are trending in the right direction."