Orlando (35-25) is tied with Atlanta for fifth in the Eastern Conference, and clinched its sixth consecutive trip to the playoffs after beating Cleveland 100-84 on Sunday.
It was also the fourth straight game for the Magic without Howard, out indefinitely with a herniated disk in his back, and fifth without Turkoglu (facial fracture).
Van Gundy is planning to be without his All-Star center and starting forward for the rest of the season and the playoffs.
"We're approaching it that the 13 (healthy) guys we have now are who we're going to have the rest of the season and in the playoffs," Van Gundy said.
The Magic suffered another blow when reserve Glen Davis, filling in for Howard, exited Sunday's win with a sprained right knee. He'll undergo further examination, but there's no timetable for a return.
"He hyperextended his knee, so my guess would be that he'd not play," Van Gundy said. "I haven't been told anything officially, though."
With the injuries piling up, Orlando could use another big effort from Jameer Nelson, who had 21 points and nine assists against the Cavaliers after making just 4 of 14 field goals and finishing with nine points and four assists in a 109-81 loss to the Hawks two days prior.
Nelson is averaging 14.6 points and 7.2 assists in his last 11 home meetings with Philadelphia (31-28).
Ryan Anderson is averaging 18.2 points in his last five games versus the Sixers, including 27 in a 103-87 home victory Feb. 15. However, he has shot 21.2 percent from the floor -- 2 for 19 from 3-point range -- to total 22 points over his last three games overall.
The Magic have won 17 of their last 20 meetings with Philadelphia, including two of three this season while holding the 76ers to 81.0 points per game.
While Orlando is already preparing for the playoffs, the Sixers didn't help their chances in Friday's 95-89 loss to New Jersey, failing to secure a three-game winning streak with a defeat to a team already eliminated from postseason contention.
"'We're going to have to step up as a team and not fear it," said forward Elton Brand, who scored all eight of his points in the first quarter. "This is an exciting time. Let's keep playing, let's keep getting it together."
Philadelphia guard Lou Williams, the team leader with 15.0 points per game, has combined for 18 in his last two games. He's averaging 18.5 in his last six meetings with the Magic, and had 21 at Orlando in February.
Jrue Holiday, who scored a team-high 19 points Friday, has made just 6 of 28 shots from the floor and has totaled 14 points against the Magic this season.