Maclin left Sunday night in the first quarter with torn tissue in the bottom of his foot. He left Giants Stadium after the game on crutches.
The Eagles are on a four-game winning streak and in sole possession of first place in the NFC East after the 45-38 win over New York. The Eagles (9-4) hold a one-game lead over the Dallas Cowboys (8-5) and a two-game lead over the Giants (7-6).
"Jeremy has plantar fasciitis and he tore one of the two strands in his foot," Eagles coach Andy Reid said. "He should be OK, probably not this week, but we're hoping the following week. They say this is usually a two-week deal."
Maclin, the Eagles' first-round draft pick out of Missouri, is second on the team with 46 receptions for 623 yards and four touchdowns. He originally injured the foot in the team's win over the Atlanta Falcons on Dec. 6. Maclin missed practice Wednesday and Thursday leading up to the Giants game but was back on the field Friday and started Sunday night.
Curtis has not played since he injured his knee in a loss to the New Orleans Saints in Week 2. Last week he did practice and made the trip to Giants Stadium but was inactive.
The veteran wideout said he thought he could go Sunday night. Now, he may get the chance against the 49ers.
"We'll see how Kevin is," Reid said. "He really took quite a few reps, more reps than I thought he would last week. So that will be increased this week and we'll just see how he does. If he's not right, he's not right and we'll work from there.
"He said he felt pretty good. His legs were tired and his wind wasn't where he wants it to be, but he actually felt pretty good," Reid said.
Curtis, who had surgery in the offseason for a sports hernia, caught five passes for 70 yards in the two games he played before the knee injury.
DeSean Jackson has emerged as the Eagles' big-play threat. Jackson, also an explosive punt returner, scored his seventh and eighth touchdowns of 50 yards or more this season Sunday night, tying an NFL record shared by Elroy "Crazy Legs" Hirsch and Devin Hester.
"I'm stating the obvious here, but DeSean is playing at a very high level," Reid said. "The thing I appreciate about him the most is he loves to play the game. He gets very excited. He doesn't care how big the game is or anything else. He just goes out and plays and enjoys doing it."
Other than Maclin, Reid listed three players with injuries after Sunday's game: tight end Brent Celek (back), defensive end Trent Cole (hamstring) and fullback Leonard Weaver (hamstring). All three are listed as day to day and should play against San Francisco.