During the evening practice, Williams made a spin move after a reception and hurt the knee. He limped to the sideline, was examined by team trainers and then carted off the field to the locker room for tests.
Coach Jack Del Rio declined comment, probably realizing he would face tough questions about whether Williams returned to the field too soon after an injury.
Williams was placed on the physically unable to perform list as the team opened training camp Saturday. He said he sprained his knee running steps inside Jacksonville Municipal Stadium.
Williams missed the first three days of camp, but he was back on the field Tuesday morning wearing a protective sleeve, running routes and catching passes.
A first-round draft pick from Washington in 2004, Williams had his most productive season last year. Although he caught just 38 passes, he averaged 16.6 yards a catch and had 10 touchdowns.
Porter, who signed a six-year, $30 million contract in February to be the team's No. 1 receiver, had surgery nearly two weeks ago to repair a torn hamstring and will miss at least the entire preseason. Meester injured his right biceps Sunday and could be out even longer.
Meester was planning to travel to Birmingham, Ala., on Wednesday to get evaluated by renowned orthopedic surgeon Dr. James Andrews.