Manager Buck Showalter made the announcement following today's 7-7 tie with the Pirates at Ed Smith Stadium.
Showalter said Machado being on the active roster on opening day is "not realistic."
Machado underwent surgery on his left knee in October. He was cleared to start running again yesterday after being bothered by a mild strain in his left calf and having scar tissue break up in his knee.
The DL assignment can be backdated to yesterday, making Machado eligible to come off the disabled list April 6. He would miss five games if ready on that date, though Showalter didn't set a timetable for the third baseman's return.
Machado could play games at Single-A Frederick, Double-A Bowie and Triple-A Norfolk. He also could continue his rehab "inside our locker room," Showalter said.
Showalter convinced Machado that it would ease some pressure and clear his head if reporters found out today that he was headed to the disabled list. No more questions about the possibility of being ready on March 31.
"He's miserable in a lot of ways," Showalter said. "Quite frankly, he likes our guys, but he's tired of watching."
Showalter may have held off making a decision if Machado had been pain-free and already cleared to run immediately after returning Thursday night from an appointment with Dr. Neal ElAttrache in Los Angeles.
Also, Zach Britton is fine. A miscommunication led to head athletic trainer Richie Bancells coming to the mound in the eighth inning. Showalter was signaling for the umpire while intending to remove Britton, who reached his pitch count.
Update: Machado left the complex before reporters were allowed inside the clubhouse. Executive vice president Dan Duquette will address the media Monday morning.
"Manny felt good today, a little better than yesterday," Showalter said. "I think that the thought
of him starting the season on the active list is probably not realistic. I don't think that's a big revelation to anybody, but it will probably be portrayed as such.
"I was talking to him today about going forward, potentially staying here. He gets 20 days once he's ready to play, which means he could play down here until he's ready to go out. We've got a pretty good idea about how much time it would take, and then we'll look at the Bowie, Norfolk, Frederick schedule. We may even work him out of our locker room. I think that's probably where we're headed. But he's made a lot of strides. He's getting close. It's almost completely gone today, so I think it's good for him to kind of start getting in that frame of mind now.
"He's miserable in a lot of ways, OK? It's the first time in his life at 21, 22, he's looking out there and watching people play baseball. Quite frankly, he likes our guys but he's tired of watching. I think to start talking about getting in games and (playing under) lights, he can play in all the extended spring games he wants to, but once he goes to a place where there's people paying to get in, I'm hoping it's X-number of games down here in extended spring.
"Somebody said, 'Well, there's maybe not any games going on there.' Oh, there'll be games. We'll make games, and then when he goes out, the clock starts ticking."
Showalter and Machado knew this day was coming.
"I don't obviously reveal everything," Showalter said. "We knew. He knew. He knows the level that he has to be at to perform in the big leagues, and we want to get it right the first time. He knows how much all of our guys mean to our club, so when we get him, we want to get him right. He wants to be fair to everybody.
"I think it's almost, I don't want to say a relief, but at least to know this isn't a failure by any stretch. I still think you're going to get him sometime in April. For us to get out of here and everything kind of stop a little bit, I think when he gets a couple games under his belt, I think it'll move quickly because he'll quit thinking about all the moving parts.
"From here on out, the next time you'll see him will be in Frederick, Bowie, Norfolk. We're going to take a look at the schedule and weather. He may even work out, like I said, out of our locker room."
Showalter was asked if anything happened within the last few days to bring about today's announcement.
"I think his face," Showalter replied. "He got back, he's doing everything. I just want to make sure we're focused on... it's a long, long season. I think he's going to play a lot of games this year for us.
"I think the mental message is as important as the physical.
"If he had come back and been completely pain-free and running... I want that doubt completely gone. I wouldn't be surprised to have him come in here tomorrow and maybe have his best day physically. But I know in some people's minds it was a foregone conclusion. I like where he is. If you had told me coming into the spring that this is where we'd be with the surgical side and everything, I would have been fine with it."
The original timetable following the surgery was four to six months.
"Yeah, so try to keep that in mind," Showalter said. "We didn't want to throw a wet blanket on it, because you don't want to underestimate the human body, especially Manny's, but he'll be fine.
"I was just sitting there in the fifth inning and said, 'What do you think we just go ahead and put this out there, so you can just quit answering it?' He said, 'I don't care.' But then you can get on with knowing what the end game is and knowing what you've got ahead of you. He needs to know, too.
"Think about it. He's walking in here and trucks are leaving for Baltimore and players are getting ready and he's just looking forward to taking infield in BP and that's it, just standing around watching the game. I saw him out there today at lunch just kind of jogging by himself, wondering what might be going through his head. That kind of put me over the hump on it, too.
"I haven't talked to anybody upstairs. I talked to Richie about it. I think it's the right thing to do, by God."