GEORGETOWN, Ky. — The Bengals sustained their first significant injury of training camp Monday when tight end Reggie Kelly ruptured his Achilles’ tendon, a notable setback to an offense that finished last in the NFL.

Kelly hurt his left leg during a morning practice and will have surgery on Wednesday. He is expected to be sidelined for at least six months. It is the first major injury for Kelly, an 11-year veteran who has spent six seasons with Cincinnati.

The injury occurred when the tight end moved sideways during a non-contact drill.

‘‘It’s very unfortunate,’’ offensive coordinator Bob Bratkowski said. ‘‘We lost a very good player who is a true professional, a leader and a gentleman. There’s nothing we can do about it. It’s a freak thing. We have to face it, go forward and find a way.’’

Kelly finished third on the team in receiving last season with 31 catches for 207 yards. The injury opens the way for Ben Utecht to take a larger role. Utecht was hurt for much of last season, when he caught only 16 passes. Kelly is considered the better run blocker, and the Bengals are committed to restoring their running attack this season.

Cincinnati finished last in the league on offense last season largely because the offensive line struggled to open holes and protect quarterback Carson Palmer, who missed a dozen games with an elbow injury. The Bengals have revamped the line — right guard Bobbie Williams is the only lineman returning in the same spot.

The Bengals were counting on first-round pick Andre Smith to start at right tackle, but he hasn’t reported for camp because of a contract holdout. Smith has missed the first four days of practice.