On Tuesday, an MRI revealed that Ortiz did not tear or rupture the tendon. He wore a walking boot on his right foot as a precaution. The Red Sox's DH suffered the injury in the eighth inning of Monday's 5-1 win over the White Sox when he stepped on second base while rounding the bases on Adrian Gonzalez's three-run homer.
"Lots of pain," Ortiz said. "Today was worse than yesterday when it comes down to soreness. But it's not torn, which is good."
Ortiz guessed that he would be sidelined for about one week, though he will seek a second medical opinion on Wednesday in Miami before deciding whether he needs to go on the DL.
"We'll wait at least 24 hours and probably into tomorrow, maybe until we get a second opinion," said Red Sox manager Bobby Valentine.
Ortiz missed nine games last season with bursitis in his right heel, but he said Tuesday that the two injuries are not the same.
"This is different," Ortiz said. "It's in the same area, but different. I've got a little bit more soreness initially."
Ortiz was confident the injury would not end his season prematurely.
"No. I didn't feel any pop, which is the first thing the doctor asked," he said. "I didn't feel any of that."
Boston's latest injury comes just as the club's health was improving. Carl Crawford made his season debut Monday in left field, and Jacoby Ellsbury has played in every game since the All-Star break following a three-month absence.
"I like to be on the field, that's me," Ortiz said. "Right now we're in a good situation with everybody coming back. It's crazy. One come out, another one goes in. It's like a roller coaster. Hopefully it doesn't take too long."
Ortiz has been the most consistent hitter for the Red Sox this season. He leads the team with a .316 average, 23 home runs, 58 RBIs, 101 hits and a .414 on-base percentage.Without Ortiz, the Red Sox will rotate players at DH.
"I don't see one person sticking out as someone we're going to put there and say, 'He's replacing David Ortiz as the designated hitter.' You don't do that," Valentine said.
Austin Laymance is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.