The team said Saturday that Lopez was hurt during its 121-120 overtime loss at Philadelphia on Friday. The Nets said they would issue another update next week after consultation with their doctors.
Lopez had the same injury, a fractured fifth metatarsal, when he was limited to five games in the 2011-12 season. He underwent surgery following last season to replace a bent screw in the foot.
Lopez is averaging 20.7 points and 6.0 rebounds in 17 games. He has missed nine with a sprained left ankle.
Though was no indication he was seriously injured Friday, when he played 44 minutes.
The 7-footer from Stanford didn't miss a game during his first three seasons in the NBA, but hasn't made it through a full season since. He missed seven games last season when he sprained the same foot.
The Nets are just 9-17 after entering the season with huge expectations. They have Andray Blatche and Reggie Evans as possible replacements on the bench, or could move Kevin Garnett to the centre position, as the Boston Celtics did last season.