McDonald’s second pitch of the game sailed to the backstop, which brought the trainer and manager Rick Renteria to the mound. McDonald quickly exited in favor of right-hander Yao-Lin Wang.
"He was shaking his arm, so I went out there and he said it didn't feel right," Renteria after the game, which the Cubs lost 6-2.
McDonald’s status is uncertain at this point.
"We don’t know," Renteria said. "We won't know until he's evaluated."
McDonald signed a one-year, $1 million (non-guaranteed) contract with the Cubs in February after an injury-riddled season in 2013. He had shoulder problems limiting him to six starts with the Pittsburgh Pirates last season.
McDonald has struggled all spring, amassing a 12.71 ERA in 5.2 innings. He was in competition for a starting role with Jake Arrieta unable to start the regular season on time due to shoulder stiffness.