Colston said he had a torn ligament resulting from a play Sunday when he reached forward to make a catch while taking a helmet-first hit to his hands from Ronde Barber.
"I don't know if my thumb just got caught in an awkward position. It just bent all the way backward," said Colston, who was wearing a cast over his left hand. "I guess the only silver lining is that I'm going to have a chance to come back and play a good portion of the season and hopefully be back in time for that playoff push."
Colston tried to continue playing with the injury during the Saints' 24-20 victory over Tampa Bay but finished with only three catches for 26 yards. He made one catch after the injury.
Colston was a seventh-round draft choice out of Hofstra in 2006. At 6-foot-5, 225 pounds, he provides quarterback Drew Brees a big target and emerged as one of Brees' favorite receivers during his rookie year. Colston went on to compile 2,241 yards receiving for 19 touchdowns in his first two seasons.
His 168 catches are more than any NFL receiver has had through only two seasons. During the summer, Colston agreed to a three-year contract extension that could keep him in New Orleans through the 2011 season.
"It's tough, especially when you lose a guy as productive as him," Brees said after Wednesday's practice. "But there's always an opportunity for a younger guy to step up or guys that might not get as much playing time ordinarily to step up and contribute even more.
"I'm confident with all our guys. However we piece it together, whoever is on the field knows what to do and they know they'll get their opportunities," he said.
Most of Brees' 343 yards and all three of his touchdown passes in the victory over Tampa Bay involved receivers other than Colston.
How much tougher it is for other receivers to get open without Colston drawing double coverage remains to be seen. But the Saints also have a new receiving threat in tight end Jeremy Shockey, who made his debut last Sunday with six catches for 54 yards, including a drive-extending 10-yard catch on third down that set up a field goal.
"It was good for him to come out and play as many snaps as he did and make six catches, some of them very big, and third-down conversions," Brees said. "Certainly, he's a guy I'm not going to shy away from for any reason even if we haven't gotten as much time together as we hoped we would have through training camp, the preseason and such."
Colston's absence is expected to open the way for Robert Meachem to dress for a regular-season game for the first time since being drafted in the first round a year ago. New Orleans visits Washington on Sunday.
"You see the smile on my face? It's a dream come true," Meachem said. "I'll do whatever it takes to make my teammates and coaches proud and so my family back home can hold their heads high."
Meachem, who had a solid preseason that included a 60-yard touchdown and a 49-yard catch, was not sure why he was left off the active roster in the opener. The active receivers in the game were Colston, David Patten, Lance Moore, Devery Henderson and Terrance Copper. Copper and Moore both also play on special teams.
"Coach, he felt comfortable with the five guys who were at receiver. He's been in the league a long time, so he knows what he's doing. I didn't second-guess that," Meachem said. "Being a competitor, I wanted to be out there. It hurt not being out there, but we got the victory."