Ortiz was removed from the lineup prior to the start of Boston's doubleheader against Tampa Bay on Tuesday because he could not run without feeling pain.
He said he first began to feel the bursitis during a game Sunday against Seattle.
"The doctor wants me to rest for three to four days," said Ortiz, 35, who wore a boot on his right foot Wednesday to restrict movement. "The doctor said it's pretty normal in people that exercise. They deal with that every day. It's just aggravation from running."
Ortiz has a batting average of .300 this season with 24 home runs.