"The doctor didn't even really know. The doctor was at first [saying] concussion. Then after he examined him, he's like, 'He might be sick,'" Indians manager Terry Francona said. "On the second day, when the fever starts to go away but he still had the headaches and the light, it became obvious that we better treat it like that, because the other end of the spectrum is you play a guy, and that's not good."
Santana said he was feeling dizzy and had difficulty sleeping. However, he also noted that he felt much better on Friday.
"I don't feel uncomfortable like two days ago. Right now I feel much better," Santana said.
Santana will now begin the process of getting medically cleared to return to the field. In addition to feeling symptom-free, he will also have to reacquaint himself with the bright lights of a baseball stadium, which the team plans to address by bringing him into the dugout for part of Friday night's tilt with the Rockies.
"He's going to stay for three innings tonight, sit in the dugout, by plan, then come back in [the clubhouse]," Francona said. "As long as he tolerates everything, we'll keep increasing that. It may not seem like a big thing, but again, got to go steps."
Santana, batting just .159/.327/.301 this season, had four hits in his last 12 at-bats before the injury.
Fellow injured batter Nick Swisher, meanwhile, has begun rehabbing his knee by taking part in some cross-training. The team has refrained from having him take any swings, but hopes he can progress beyond the pool by Monday.
"Everything he's doing right now is in the water," Francona said. "They want to get him symptom-free, and I think he's getting towards that. Obviously, the water takes the load off what you're doing."
Jordan Bastian is a reporter for MLB.com. Read his blog, Major League Bastian, and follow him on Twitter @MLBastian. Alec Shirkey is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.