Kelly said he is not sure how long Kelce will be out for, but FOX 29 TV's Howard Eskin reports the center could miss up to two months.
Kelce left Sunday's win over Washington with an abdominal strain. He was replaced by David Molk.
Kelce was a sixth-round pick in the 2011 draft and has started all 37 games he has played during his career.
The Eagles will play the San Francisco 49ers on the road on Sunday.
- Paul Palladino