"Right now the prognosis is four weeks to come back," Hoyer said Wednesday afternoon. "We're not going to shut him down. His mentality is he can beat four weeks and come back."
Castro, 24, injured himself sliding into home in the first inning of Tuesday's 7-1 win over the Milwaukee Brewers as his cleat got caught in the dirt around home plate. He limped off under his own power and X-rays showed no fractures. He underwent an MRI to rule out any ligament damage.
Castro was unavailable for reporters on Wednesday afternoon as he was receiving treatment on the ankle.
"(His) spirits are up and he said 'I'll be back,'" manager Rick Renteria relayed.
Castro made his third All-Star team this season and was hitting .292 while already tying a career high in home runs with 14.
"In my mind's eye he's had a very productive season," Renteria said. "He's dealt with a lot of different things very positively. He's worked extremely hard."
Castro was criticized often last season as he struggled to a .245 batting average but got into the best shape of his career over the winter. A hamstring injury caused him to miss most of spring training and slowed his start to the season but as he got healthy he took off.
Late last month he went on the bereavement list after a car accident in the Dominican Republic claimed the lives of several people close to him. He missed his first five games of the year but came back playing well. He has a nine game hitting streak after Tuesday's first inning single but that might be the last hit of his season.
Second baseman Javier Baez will move over to play shortstop, the position he played almost his entire minor league career.
"Right now our shortstop goes down and we can feel really comfortable," Hoyer said of Baez.