It isn't clear what Smith is seeking treatment for, but the news comes days after a Periscope video surfaced that shows an unidentified man and woman talking about a hand-rolled cigarette.
Smith's decision to enter a treatment center was first reported Friday by TMZ Sports.
Smith is currently serving a yearlong suspension handed down in November for violating the NFL's substance-abuse policy. He will be eligible to apply for reinstatement in September, 60 days before the one-year anniversary of the suspension.
"I heard the same information, but I haven't technically checked with the front office," Raiders coach Jack Del Rio said when asked about the Smith reports. "It doesn't matter for me at this point. There's a process that he's involved in that I can't be a part of. A November (return) is the earliest I can hope for, and I remain hopeful for the young man to get himself and his life turned around. If he can get his ducks in a row, as a football team we would invite back a good football player. The first thing for him is to make sure he's taken care of. The focus should be on him getting the help he needs to get his life in order so he can have a good life."
Asked if he has had any contact with Smith, Del Rio said, "I'm hoping for the best from a distance, because I can't be directly involved."
At one point in the video posted online earlier this week, the woman tells the man that he "shouldn't even be posting that" and that he is "hella stupid" as the man holds the lit cigarette.
The video cuts off immediately after the man says, "They don't know it's me. It's not like I put 'Aldon Smith.'"
Smith had tweeted an apparent denial that it was him in the video. Smith had previously been to rehab, in 2013, following two DUI arrests.
ESPN's Ed Werder had reported that because of the video, the NFL will investigate whether Smith had violated the protocols required of a suspended player seeking reinstatement to the league following a violation of the substance-abuse policy.
"As a teammate and friend, the only thing I can tell him is anything he needs, let me know and I'll have his back," Raiders fullback Marcel Reece said. "If someone needs rehab, then that's exactly what they need and I pray for Aldon that he gets any and all help that he needs. All football aside, just want him to get help if he needs it. And when all is said and done and he's ready to come and join this team, as a team we're going to welcome him back and we're going to win a championship. That's what our goal is. But as a man and as a friend, we just want to help him and pray for him and do anything we can to help him if he needs it."
Information from ESPN's Paul Gutierrez was used in this report.