Machado was injured in the seventh inning. After making a backhanded stop of Nick Van Stratten's ground ball deep in the hole, he made a leaping throw from the outfield grass to record the out. He was helped off the field by trainer Pat Wesley.
According to MLB.com, Machado was removed for precautionary reasons.
The third overall pick in last year's Draft capped the Keys' five-run second inning with a three-run double that extended his hitting streak to seven games. He added a single in the seventh and is batting .237 with two homers and eight RBIs in 17 games since he was promoted from Class A Delmarva.
Machado rejoined Frederick on Wednesday after going 0-for-2 for the U.S. team at the All-Star Futures Game. The Miami native called the experience a dream come true.
"Once I got drafted in 2010, I said, 'That's my goal. I want to play in the Futures Game,'" he told MLB.com. "I didn't think I was going to make it after I got injured. I bounced back from the injury. I did well for a week and a half. I'm grateful for that."
Machado, who turned 19 on July 6, was sidelined for a month after sustaining a patellar subluxation while at Class A. But he still batted .276 with six homers, 24 RBIs and 24 runs scored in 38 games in the South Atlantic League.