The Cubs called the injury a "moderate' strain," which is typically a four-to-six-week injury. The Cubs will re-evaluate Contreras in about two weeks, once he is deemed pain free.
On Friday, Contreras said he felt bad he couldn't be out there to support the team.
"I'm going to take it slow," Contreras said. "I'm going to make sure when I get back I can play with 100 percent. The next day [Thursday] I could walk normally and today [Friday] I feel a lot better."
The news of the strain correlates with what Contreras was telling teammates and others after the injury, believing he escaped the worst. Contreras, 25, pulled up lame a few feet from first base after hitting a grounder to third base in the eighth inning of the Cubs' 3-1 loss to the San Francisco Giants. He was on the ground for a few minutes before being helped off the field.
"Obviously it's difficult not to have his name in the lineup tonight, with all the wonderful things he's done all year, especially since the All-Star break," Cubs manager Joe Maddon said before Friday's game.
Kyle Schwarber, who was lost for the season in Game 3 in Arizona last year, knows what it feels like to rally around an injured teammate.
"We're going to miss him, but we have a lot of confidence in this lineup," he said. "Collectively, as a group, when someone goes down we always pick them right back up. It's not what we wanted to happen, but we have to keep going forward and look forward to getting him back."
Contreras was one of the hottest Cubs before he went down. He has 21 home runs and 70 RBIs this season.