The Giants’ loss to the Dallas Cowboys on Sunday felt even worse yesterday, when it was disclosed that three key players could miss time with injuries. But the Giants say the injury that could have been the most devastating — to Eli Manning’s throwing shoulder — is not serious.

Reports surfaced yesterday afternoon that Manning suffered a separated throwing shoulder that would keep him out for a month or more, but later in the day the Giants said Manning’s injury was not that serious, and that if he can continue to throw despite pain in the shoulder, he could play Sunday against the Green Bay Packers. The 45–35 season-opening defeat in Dallas saw two other key players, running back Brandon Jacobs and defensive end Osi Umenyiora, suffer knee injuries that could cost them significant playing time.

But yesterday’s big story was the health of Manning, who injured the shoulder when he was sacked on a two-point conversion attempt in the fourth quarter. Manning stayed in the game for one more possession after that — a possession on which he threw four short passes, all complete, the last for a touchdown to Plaxico Burress — and then was replaced by backup Jared Lorenzen.

If Manning can’t play Sunday, Lorenzen will start, and seeing him under center wouldn’t give Giants fans much confidence that the team can avoid an 0–2 start. The Giants signed Lorenzen in 2005, but he had never thrown a pass in a regular season game until he replaced Manning Sunday, and Lorenzen is best known to football fans not for his passing ability but because he is the NFL’s heaviest quarterback. The Giants list Lorenzen at 285 pounds, but he probably weighs more than that. During his college years at Kentucky, his girth earned him nicknames such as “Hefty Lefty” and “Pillsbury Throw-Boy.”

Big Blue’s only other quarterback is Anthony Wright, a nineyear veteran who has started 19 games, mostly with the Baltimore Ravens. If Manning can’t play and Lorenzen proves ineffective, Wright, who also played for the Pittsburgh Steelers, Dallas Cowboys, and Cincinnati Bengals, would be the next man up.

If the shoulder prevents Manning from throwing for a significant period of time, the Giants may decide to sign another veteran quarterback, but there aren’t many options available. Tim Hasselbeck would be the most likely choice because he spent the last two seasons and this year’s training camp and preseason with the Giants and already knows the offense. Tim Rattay, who was recently released by the Tennessee Titans, would also be a possibility.

Byron Leftwich, whom the Jacksonville Jaguars cut prior to the season, is by far the best quarterback available right now, but Leftwich will want to sign with a team that will make him its quarterback of the future, and that will prevent him from joining the Giants.

Any time a quarterback injures his throwing shoulder it’s a serious concern, but Manning’s injury may be less significant than the knee injuries suffered by Jacobs and Umenyiora, both of whom are likely to miss a month.

Jacobs, who was supposed to emerge this season as the successor to Tiki Barber, had his knee bent awkwardly when he was tackled on a carry in the second quarter. Umenyiora, the Giants’ best pass rusher, left the game on the Giants’ first defensive series. There is no definitive word on how long Umenyiora will be out. The Giants said their medical staff will continue to monitor him this week.

The big question surrounding Jacobs heading into the season was whether he could be as durable as Barber, who missed only six games in his 10-year career. That he couldn’t even make it through the first half of his first game as the Giants’ starting running back is not a good sign, but backup running back Derrick Ward played very well in Jacobs’s absence, carrying 13 times for 89 yards and catching four passes for 27 yards. Ward, in his fourth year with the Giants, has been used almost exclusively on special teams — he had just 35 rushing attempts in his first three seasons. But the Giants’ coaches like Ward, and if he can play for the next month like he played Sunday, the Giants’ running game will be in good shape.

Jacobs’s absence may also mean an increased workload for Reuben Droughns. When the Giants traded for Droughns in March, he was expected to compete with Jacobs for the starting running back role. Instead, after blocking fullback Jim Finn was injured, the Giants’ coaches moved Droughns from running back to fullback, where he played Sunday night. While Jacobs is out, Droughns will almost certainly get the ball more often, and although the Giants’ coaches did not seem impressed with Droughns in training camp, he is only two years removed from a 1,232-yard season with the Cleveland Browns. Overall, the Giants’ depth at running back means they should be able to withstand Jacobs’s absence.

The situation at defensive end is more complex. Umenyiora has led the team in sacks the last three years, so he will clearly be missed if he is out for a significant portion of the season, but if Michael Strahan can play at a high level despite skipping all of training camp and the preseason, he and Justin Tuck can give the Giants a solid pair of defensive ends. There is also the option of moving linebacker Mathias Kiwanuka back to defensive end, his natural position, although the Giants’ coaches seem committed to keeping Kiwanuka at linebacker despite his shaky performance Sunday.

In the end, Umenyiora and Jacobs are much more replaceable than Manning. For all the grief Manning gets from Giants fans, few want to see Lorenzen take the field against Green Bay.

Mr. Smith is a writer for FootballOutsiders.com.