Britney Spears' Knee Injury Delays Video Shoot, "Tonight Show" Appearance

It looks like it's dangerous on the top of the charts.

Britney Spears, who is still riding high atop the Billboard album chart, had to cancel her next video shoot and return o her home in Louisiana Wednesday after injuring her knee.

The singer twisted her knee while rehearsing some dance moves last week. The injury will not require surgery, but Spears has already undergone some physical therapy in Los Angeles. The incident has also forced Spears to cancel an appearance on Wednesday night's edition of "The Tonight Show with Jay Leno." That appearance is being rescheduled.

The injury occurred on Friday when Spears was running through steps for her new video, "Sometimes." The conceptual video will be directed by Nigel Dick, who also shot her video for "Baby One More Time."

The new clip will feature Spears on the porch of a beachfront home watching a group of kids having fun, prompting flashbacks about her former boyfriend. Spears is expected to begin touring sometime

in July.