The Cubs initially said Castro would be out seven to 10 days after he suffered the injury on March 2, but now there is no timetable for his return.
"I don't have a set date in my head right now," Renteria said. "That's all based on how he's progressing. He's progressing well."
Castro said it could be another week because he's only running "40 percent," according to Rogers.
"I don't want to rush myself," Castro said. "If I can play in 10-12 games in spring training I think I'll be good for the season."
The Cubs open their season on March 31 against the Pirates.
The 23-year-old Castro's production has dropped off precipitously the last two seasons. He was a .307 hitter in 2011, but dropped to .283 in 2012 and .245 last season. He saw an increase in strikeouts and declines in OPS, runs and steals.
The two-time All-Star also said he'll be placing more of an emphasis on his speed game this year after stealing only nine bases last season.SI WIRE: Manny Ramirez admits PED 'mistakes,' still wants MLB shot