The reigning NFL Defensive Player of the Year was not present as Rams players were due to report by 1 p.m. ET. Practice begins Thursday.
A first-round pick in 2014, Donald is entering the final season of his rookie deal and is scheduled to earn $6.9 million. If he does not report to camp by Aug. 7, he will remain a restricted free agent after the season.
Last season, Donald reported on the eve of the opener -- without a new contract in place -- and was activated in Week 2.
"Each situation is different. Different players, different agents," general manager Les Snead told reporters Tuesday. "You work on everything simultaneously, but you really don't know when you're going to get something done or not because it's case by case."