Calling it the most difficult roster decision of his career, Miami Dolphins Coach Jimmy Johnson released veteran linebacker Jack Del Rio yesterday. "Jack is a true professional. He's intelligent, a competitor, and a team player," Johnson said.

Del Rio, 33, then decided to retire. "I'm not going to move my family around the country anymore," said Del Rio, who played with five teams in his career. "We're going to leave football now and we will get on with the rest of our lives."

Del Rio said he understood the decision and expressed no hard feelings.

"I thanked him for the opportunity," Del Rio said. "I came in and played hard and I thought I competed well. I appreciate having one last shot at giving all I had."

The release of Del Rio, who was in his first season with Miami, was made because of the solid play of rookie Zach Thomas, now the starting middle linebacker. Thomas led the team with eight tackles in last week's preseason opener against Tampa Bay.

"The bottom line is that Zach Thomas was making plays," Johnson said. "He has quickness, he's an instinctive player, and he makes plays . . . Jack Del Rio would still be here and still be our starter were it not for the play of Zach Thomas."

Thomas, a fifth-round pick from Texas Tech, is small for a linebacker at 5 feet 11, 231 pounds, but is extremely quick.

Meanwhile, wide receiver Fred Barnett underwent reconstructive surgery to repair a torn ligament in his right knee, the team said. No timetable has been set for his return. The injury was discovered two weeks ago during arthroscopic surgery to repair torn cartilage in the same knee. At that time, Barnett was also found to have a torn anterior cruciate ligament. Barnett, 29, signed a five-year, $8.5 million free-agent contract with the Dolphins in March. 49ERS: Middle linebacker Gary Plummer underwent successful surgery to repair his broken left wrist. He will miss 4-5 weeks. EAGLES: Wide receiver Mark Ingram suffered a slightly fractured right eye socket in Saturday's loss to Baltimore, and is expected to miss three weeks. BENGALS: Cincinnati signed defensive end Jevon Langford, its fourth-round pick out of Oklahoma State, to a three-year contract. In addition, the Bengals waived cornerback Nick Ferguson, a rookie free agent out of Georgia Tech. COLTS: Team owner Robert Irsay has been hospitalized for pneumonia. Irsay, 73, entered an Indianapolis area hospital on Friday and was expected to stay about a week, said his wife, Nancy Irsay.