Does capsule injury last for up to 4 weeks? i feel pain when extending my knee horizontally and my orthopedic doctor told me capsule knee injury.

Can take 4-6 weeks: If you have a soft tissue capsule injury to the knee it can certainly take 4-6 weeks to heal 'but many times when you get that type of injury you may also injure the meniscus or other ligaments in your knee you should have a good exam and possibly an MRI before returning to sports.

Capsule injury: It could last that long but i would consider an MRI soon if no further improvement.