Improvement had been steady, enough for Diamondbacks center fielder Adam Eaton to be encouraged by the progress of his left elbow. He recently began a rehabilitation stint in the minors and as he started to make more throws, his arm held up fine. Even his swing at the plate was better. But a potential return to the Diamondbacks was put on hold after Eaton sent a throw to home plate Monday in his first start with Triple-A Reno. “It didn’t feel as well as it should have,” he said. Eaton suffered a tear in his ulnar collateral ligament during spring training. He came back to Phoenix on Wednesday for a visit with team physician Dr. Michael Lee and received an MRI that showed no new damage to the ligament, but there is some fluid around it. “The UCL isn’t any worse,” Eaton said. “They said it looks good, but there’s just a little fluid in there which would cause some irritation. As of right now, we’re going to take off about three weeks and then re-evaluate from there.” Eaton is set to receive a second opinion from Dr. James Andrews on Tuesday. “It’s a three-week period where I can continue to get stronger in my arm and learn from this,” he said. “As tough as it is, as young as I am, I’ve never tasted any kind of adversity like this before. So it’s definitely going to be a learning process for me to kind of take a step back and learn day-to-day how I can be patient and get healthy.”