Machado had an operation in October to repair a torn ligament in his left knee. The All-Star third baseman hoped to return for the March 31 opener against the defending champion Boston Red Sox, but he hasn't run in five days.
''It's scar tissue that flared up and got a little sore and we decided not to push it, which is what we talked about all along,'' manager Buck Showalter said Saturday.
The 21-year-old Machado was supposed to have an appointment Tuesday to re-evaluate the injury, but that visit will be postponed.
''There's no sense in doing that until he can really show them what he can do running,'' Showalter said. ''So that's got to get cleared up first, where he's back running again.''
Machado played in every game of the 2013 season before the injury, which occurred on Sept. 23 when he stepped awkwardly on first base in a game at Tampa Bay. He finished with a .283 batting average, 14 homers, 71 RBIs and 51 doubles.
Recovery time from this type of surgery is usually around six months, so the Orioles knew there was a chance that Machado would miss the start of the season. Now, it appears that might be reality, even though Showalter won't yet acknowledge as much.
''I'm not there yet. I'm not going to throw that wet blanket over that yet. I know Manny's not,'' he manager said. ''In four days we can get Manny more plate appearances (in minor league camp) than guys over here are going to break camp with.''
Showalter wants Machado fully healthy when he finally returns - whether it's opening day or late April.
''We are not going to push it to the point where it ends up being something,'' Showalter said. ''We want to resolve this.''