He'll have a bone chip removed, the team said. His knee was injured during a game against the Pittsburgh Penguins on Sunday.
"Certainly we're going to miss Alfie ... we're obviously a better team when he's in there, but it's a great opportunity for us to prove that we're different this year," said coach Craig Hartsburg.
Ottawa plays its second game of the season at Detroit on Saturday.
The team believes a hit he took aggravated an injury from last season, dislodging the bone chip and causing it to float around in the knee.
Though Alfredsson skated this week and didn't feel awful, he still felt some discomfort, Hartsburg said. Doctors said Alfredsson could play through it, but would eventually need surgery.
"We thought and he thought that this was the best time," general manager Bryan Murray said. "He'll miss the season-opener here but we're hoping it won't be much longer than that."
Alfredsson has two assists in two games. The 35-year-old winger had 89 points (40-49) in 70 games last season.