Machado's leg buckled when he reached the first-base bag in the seventh inning of Monday's 5-4 loss that completed a four-game sweep at the hands of the Rays.
Baltimore manager Buck
Showalter had no immediate update on Machado's injury after the game as the team awaited test results. Machado will undergo an MRI on Tuesday.
"I'm sure we won't get a full diagnosis until we get an MRI back in Baltimore (on Tuesday)," Showalter said while acknowledging that "it certainly doesn't look very promising right now."
The Orioles had another injury scare in the bottom of the seventh inning when Alexi Casilla, playing second base, collided with right fielder Nick Markakis while chasing Wil Myers' two-run single. Casilla actually caught the ball for what would have been the third out, but couldn't hold onto it when his head struck Markakis' thigh.
"I thought about doing a slide, saw him out of the corner of my eye, tried to pull up and get out of the way," Markakis said. "It was just bang bang, him coming full speed, me coming full speed. It was like trying to stop a train on a dime. I'm not a doctor or anything, but when he was out there, I could have sworn he was knocked out. He was laying there; (Adam Jones) and I were trying to get him to sit still until somebody got out there. He kind of looked dazed and confused."
Casilla finished the inning, but was taken out in the eighth.
Tampa Bay manager Joe Maddon, who had a better view of Machado's collapse, had a more stark analysis.
"It's horrible,'' Maddon said. "Hate to see that. This young man blows out his knee, possibly, and then this collision in right field. You can see how badly they wanted it, too."
Machado was in obvious pain while being treated on the infield dirt near first by team trainers and stadium medical officials. Many fellow players took to Twitter in support of Machado.
Best wishes out to Manny today for that terrible injury. Get well soon man!
— Mike Trout (@Trouty20) September 23, 2013
Showalter patted Machado several times near the shoulder before the stretcher was moved from the playing field.
"It was a tough four days and it culminated in a lot of bad stuff today,'' Orioles second baseman Brian Roberts said. "The losses and the injuries and feeling like we had a good chance coming in to Tampa, to walk out with this kind of feeling is tough for everybody."
Information from The Associated Press was used in this report.