When Washington signed Garcon, he was expected to be a vital part of a Robert Griffin III-led offense, mainly acting as the deep threat. His 88-yard reception against New Orleans is still the longest of the season.
But Garcon looks to be out at least until the bye week, per USA Today. According to the piece, Redskins Coach Mike Shannahan stated that the injury was "very much a mystery," then added:
The person briefed on Garcon's injury said it's possible Garcon could play before the bye but that the likely scenario would be for him to rest until the Nov. 18 game against the Philadelphia Eagles.
This does put the Redskins in a bind until that game (if Garcon is even able to return by then), as it prevents them from utilizing what was supposed to be one of their biggest threats on offense. Santana Moss, Josh Morgan and Leonard Hankerson have filled in well in Garcon's absence, combining for 76 receptions, 631 yards and three touchdowns on the season.
However Washington's biggest contributor in the passing game has been tight end Fred Davis, who has 23 catches for 312 yards on the season. However, Davis will miss the rest of the season due to a torn Achilles Tendon suffered in the Week 7 loss to the New York Giants (per NFL.com's Gregg Rosenthal), putting even more pressure on Washington's three top wide receivers.
Garcon will also likely have more pressure on him throughout the year as soon as he returns from the injury.
Washington's receiving corps will have to make due for at least two more games without Garcon. As for the fantasy implications, expect the continued absence of Garcon and the loss of Davis to make Griffin target Moss, Morgan and Hankerson more, while also emphasizing a running game led by Griffin and Alfred Morris.
Once Garcon comes back however, he will be expected to contribute right away, making him a good waiver-wire pickup in leagues where he's already been released, as well as attractive trade bait for anyone willing to sacrifice a spot on their bench while waiting for Garcon to come back.