There is not yet a specific diagnosis on the injury, nor a clear indication of how severe it might be. That is all expected to come into focus on Monday, when Berkman undergoes a magnetic resonance imaging scan in St. Louis.
To fill Berkman's spot on their roster, the Cardinals recalled first baseman Matt Adams, who was removed from Triple-A Memphis' game on Saturday night after Berkman left St. Louis' contest at Los Angeles.
"I wish I knew," Berkman said, when asked to give a prognosis on his knee. "It doesn't feel right. I wish I knew more than that."
Berkman did differentiate between the feeling of his knee on Saturday compared to previous knee ailments. He has had four knee surgeries already -- two on each knee. Asked if he feared this to be a tear of his anterior cruciate ligament, Berkman said he was optimistic that that isn't the case.
"There is definitely a little bit of instability that is mildly concerning, but it definitely wasn't the same kind of injury," Berkman sad. "When I did it before, it was a hyperextension. This time, my knee was bent. I'd be surprised if it is anything that major. My guess is that I have a little meniscus ding. How bad? I don't know. It's just a wait and see."
Doctors did an immediate evaluation of Berkman's knee during Saturday's game, but little can be confirmed until an MRI exam is taken.
The injury happened in the second inning, when Berkman made an inning-ending putout at first base. His knee buckled as he came off the base, as Berkman described it, and he fell onto the infield grass after briefly hobbling on his left leg.
After being examined on the field, Berkman was helped into the dugout. When he tried to walk on his own, his knee buckled a second time.
"I didn't feel a pop," Berkman said. "[The joint] just kind of slid on me a little bit. That's the best way I can describe it."
Berkman limped around the clubhouse postgame, still not bending his right knee at all.
"It's not too painful," Berkman added. "It's a weird feeling. I wish I could describe it."
Berkman was making just his fifth start since coming off the disabled list last Sunday. A left calf strain limited him to seven at-bats from April 10 to May 12. Including a first-inning popout on Saturday, Berkman was 6-for-19 since returning from the DL.
Upon exiting the game, Berkman was replaced at first base by Matt Carpenter, who later committed a key error in the loss.
While Carpenter can handle duties at first base during Berkman's absence, the Cardinals have brought Adams up to assist there, as well. Adams started Memphis' game in Las Vegas on Saturday but was pulled in the fourth inning.
Adams has hit .340 with 20 runs scored, 10 doubles, 10 homers and 27 RBIs for Memphis this season. On Sunday, he was added to the Cardinals' 40-man roster, which has one open spot remaining.
The Cardinals have already placed three players on the DL since Monday -- outfielder Jon Jay (right shoulder sprain), outfielder/first baseman Allen Craig (left hamstring strain) and reliever Kyle McClellan (right elbow strain). Outfielder Carlos Beltran was also limited for part of the week, as he has been dealing with soreness in his right knee.
"I don't want one injury on this team, but you can see these guys starting to put together that kind of attitude of, 'Here comes another kick to the gut. Now watch this, someone else is going to step in,' " manager Mike Matheny said. "I just have faith in every guy we throw out there."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.