Lopez was hospitalized overnight for tests after he was hit by Matt Wise's pitch in the eighth inning of a 7-3 victory over the Milwaukee Brewers on Wednesday night. He was expected to be released from a hospital today.

Cincinnati put Lopez on the 15-day disabled list and activated Juan Castro, who has a partially torn ligament in his throwing elbow and expects to have reconstructive surgery. Castro had been on the disabled list since July 7.

"I'm hoping I don't have to make many throws, but I'm OK with it," Castro said.

A pair of injuries and a family illness have left the Reds short-handed in the infield.

Starting shortstop Alex Gonzalez is on the restricted list, occupied with his young son's illness. The Reds don't know when he will be available to rejoin the team.

Lopez started the season in Triple-A for the White Sox and was claimed off waivers on May 21. The Reds called him up from Triple-A Louisville on July 8 to fill in while Castro tried to get his sore right elbow healed.

The elbow bothered him when he played catch on Wednesday, so Castro was planning to talk to the medical staff later this week about having surgery. When Lopez got hurt, the Reds were in a bind.

"They talked to me and wanted to see if I could (play) in an emergency," Castro said. "It's not like they're going to be really using me. I was a little bit surprised."

Interim manager Pete Mackanin plans to use him as a last resort.

"Casto can fit the bill for what we need right now," Mackanin said. "It's convenient, especially in lieu of Gonzalez's situation. He might come in tomorrow and say he's ready."

The Reds also are missing their starting catcher.

David Ross dislocated the small finger on his right hand while sliding into second base on his double Wednesday night. The finger was put back into place, and Ross was expected to be ready to play again soon.