(Jonathan Newton/WASHINGTON POST)

Rizzo said Rendon, 21, is immobilized and will see a foot and ankle specialist on Friday.

Rendon, the sixth overall pick in last year’s draft and the Nationals’ top prospect behind Bryce Harper, hit a double in the fourth inning at Class A Lynchburg. On an ensuing base hit, Rendon tried to score and fell to ground the after rounding third base. He had to be helped off the field, putting no weight on his left leg.

“They tell me his season’s not in jeopardy,” Rizzo said. “Actually this slight fracture probably heals quicker and cleaner than a bad sprain.”

While this is the first injury to Rendon’s left ankle, he has suffered others to his body. In 2009, Rendon tore ligaments in his right ankle and in July 2010, while playing for Team USA, he fractured his right ankle. Last year, at Rice, Rendon had to play the majority of his junior season at designated hitter because of a strained muscle behind his shoulder.

Rizzo said the injury to Class A Hagerstown center fielder Brian Goodwin, who was pulled in the second inning of an April 9 game, doesn’t appear as serious. He pulled his hamstring.

“He’ll be fine,” Rizzo said. “It was a leg injury.”

The Nationals chose Goodwin with the 34th pick and signed with a $3 million bonus.