Beckham underwent surgery Monday night on his fractured ankle.
Harris is expected to undergo surgery Tuesday as well.
Marshall signed a two-year, $11 million deal with the Giants in the offseason. He had 18 catches for 154 yards and no touchdowns in five games.
Marshall was injured when he attempted to make a catch deep down the left sideline and landed awkwardly. Before leaving, Marshall had two catches for 15 yards during the second-quarter drive when receiver Sterling Shepard(ankle) was injured.
The Giants had said Shepard was undergoing tests Monday to determine the extent of the injury.
Marshall, who was in his 12th season, is a five-time Pro Bowl receiver who has played with the Broncos, Dolphins, Bears, Jets and Giants.
There were high hopes after Marshall signed as a free agent this offseason, but he wasn't able to get comfortable in the offense and in a new setting.
Marshall was slowed this summer by a shoulder injury, and he didn't develop a rhythm with starting quarterback Eli Manning. Marshall struggled with drops, including a key miscue late in a Week 2 loss to the Detroit Lions.
After several more drops in a loss to the Tampa Bay Buccaneers, Marshall voiced frustration with the way he was performing. "Just not playing well right now," he said. "I haven't played a solid game since I've been here."
The Giants (0-5) will visit Denver (3-1) for a Sunday night game as they try to pick up their first win of the season.