Myles Simmons of the Rams' official site reported Donald and the team have yet to reach an agreement on a new contract and "will continue to work to reach a solution."
ESPN's Adam Schefter first reported on Donald and the Rams' continued impasse over an extension.
The Rams reacted to Donald's return on Twitter:
Since he was holding out, the Rams didn't list Donald on their 53-man active roster. Simmons noted the team will ask the NFL to grant it a roster exemption, which would allow Donald to receive his Week 1 game check.
Donald is signed through the 2018 season. He's set to make a little over $1.8 million this season before his salary climbs to nearly $6.9 million next year.
The 26-year-old could've further tested the Rams' resolve if he had carried his holdout into the regular season, but it would've come at a significant cost. According to Over the Cap's Jason Fitzgerald, Donald would've forfeited about $250,000 by not rejoining the team by Week 1 and then another $106,015 for every game he missed.
It's not like a regular-season holdout was all that necessary for Donald to prove his worth to the Rams, though. He has 28 sacks through his first three years, and Pro Football Focus' Sam Monson ranked him as the best player in the league heading into the 2017 campaign.
"The Rams defensive lineman has been a one-man wrecking crew inside whether against the run or as a pass-rusher," Monson wrote. "He has tallied a ridiculous 161 total pressures over the past two seasons, and 90 defensive stops, generating both pressure, and decisive pressure, at a completely different rate to any other defensive tackle."
Donald will be missed along the Rams defensive line against the Colts, but at least Los Angeles should have him back when it welcomes Kirk Cousins and the Washington Redskins' aerial attack in Week 2.