Tony La Russa is out indefinitely as he undergoes medical tests in Arizona, the Chicago White Sox have announced.

La Russa, 77, missed Tuesday night's game against the Kansas City Royals after participating in regular pregame activities.

"We were trying to figure out what was going on," Andrew Vaughn said. "They mentioned a few things, maybe his heart, or something like that."

Miguel Cairo will continue to manage until La Russa returns.