Umenyiora continues to be plagued by a knee injury, while Manningham suffered a concussion at the end of the first half in Monday night's game against St. Louis.
The Giants are already banged up at wide receiver. Domenik Hixon went down for the season with a torn ACL for the second consecutive year.
With Hixon out and Manningham possibly unable to play, the Giants will have to rely on a combination of Victor Cruz, the newly-inked Brandon Stokley, and rookie third-round pick Jerrel Jernigan, who was inactive the first two games.
As for Umenyiora, the Giants were hoping that the two-time Pro Bowl selection would return to the practice field this week. Umenyiora had arthroscopic knee surgery done on August 19.
The Giants travel to Philadelphia to take on the Eagles this Sunday.