Fernandez will return to Miami for further evaluation as the Marlins await more results from today's MRI in Los Angeles.
Redmond acknowledged that the team is concerned about Fernandez. Several young pitchers have recently had elbow problems and needed Tommy John surgery. Matt Harvey, Stephen Strasburg and Patrick Corbin are among the All-Stars who have had the ligament transplant operation that can take 12 to 18 months for recovery.
"That's probably what everyone is going to talk about and continue to talk about," Redmond said. "We've protected him. We've been consistent in how we've used him, with his workload. We've given him extra days. That's a question I don't think anybody has the answer to."
Fernandez, 21, is 4-2 with a 2.44 ERA in eight starts this season. He leads all of the majors with 70 strikeouts.
However, he was roughed up during his last outing against the San Diego Padres Friday night. Fernandez gave up six runs in five innings, including two home runs.
Fernandez's fastball averaged 94.6 mph over his first four innings against the Padres, but only 90.7 mph over his last two, according to ESPN's Stats & Information. He allowed four runs in the sixth inning before being removed with nobody out.
"I think you're always concerned when you're talking about elbows," Rendon said. "That's something we have to wait to find out. But I think we're always concerned about that with pitchers, especially."
Last season Fernandez made 28 starts, going 12-6 with a major league-best .182 opponents' batting average. His 2.19 ERA was second in the majors behind three-time defending ERA champ Clayton Kershaw. Fernandez struck out 187 batters and was named National League Rookie of the Year.
The Marlins recalled left-hander Dan Jennings from Triple-A New Orleans. He made 79 relief appearances for the Marlins over the previous three seasons, going 3-5 with a 2.96 ERA.
Information from The Associated Press was used in this report.