Chrissy Metz Needed Wheelchair for Knee Injury, Not Gastric Bypass Surgery

"This Is Us" star Chrissy Metz needed a wheelchair for a bum knee ... NOT because she underwent gastric bypass surgery.

Chrissy was in a wheelchair Tuesday at LAX ... because she hurt her knee in Florida during Xmas. She has some lingering pain but should be at full strength in a few days.

The wheelchair suggested she might've actually gone through with the surgery ... after her character, Kate Pearson, vowed in the last episode to have gastric bypass. Her people tell us she absolutely did not have gastric bypass.