The Rams initially signed Walker in March, but they released him in June at least partly so that he could take care of accusations of sexual assault in Lafayette, Louisiana, stemming from an incident on the night of Feb. 28. A grand jury decided not to bring charges against Walker on Aug. 2, citing a lack of substantial evidence.
Walker, who was practicing with the Rams by Wednesday afternoon, enters as a rotational player for a defensive line that is in need of replenishing some depth. The 27-year-old has compiled 3 1/2 sacks and 63 tackles while playing in 42 games (13 starts) for the Saints and Lions from 2012 to 2016.
Walker trained with Rams inside linebacker Alec Ogletree until he reported to training camp in late July, then spent the first three weeks of August training at his old high school in Louisiana.
"I stayed in contact with some of the guys and we talked," Walker said. "I'm just happy to be here, man. This is a great organization with a lot of good guys. I'm just happy to be back."
Dominique Easley, projected to be one of three starting down linemen, tore his ACL early in training camp and will not play in 2017. Donald, widely considered the game's best interior lineman, is still holding out while in hopes of attaining a more lucrative contract.
The Rams still don't know when Donald will show up, but it isn't expected to happen this week and it may not take place before the Rams wrap up their preseason schedule on Aug. 31. A source recently told ESPN's Adam Schefter that Donald's holdout may even spill into the regular season.
Donald and Texans left tackle Duane Brown are the only camp holdouts still unaccounted for. Left tackle Donald Penn returned to Raiders practice on Wednesday, and Steelers running back Le'Veon Bell indicated via Twitter on Tuesday night that he will return to his team by Sept. 1.
Rams coach Sean McVay said earlier on Tuesday that there have been "active conversations" between Donald's reps at CAA and the key members of the team's front office.
"We'd love to have Aaron here; we'll welcome him back with open arms if that does happen," McVay said. "But in the meantime, guys are finding ways to get better and kind of just moving forward one day at a time."