Soriano grabbed his left leg a few steps from first base as he ran down the line on a groundout against Houston's Aneury Rodriguez to end the inning. Assistant athletic trainer Ed Halbur escorted Soriano off the field, and Blake DeWitt took over in left.
"It's unfortunate to see Sori go down like that," DeWitt said. "I haven't heard anything, but hopefully he's all right. He's a big part of this team. It's a tough loss today."
The Cubs have dealt with multiple injuries lately. They placed Jeff Baker on the disabled list earlier Monday, and he joined Reed Johnson (back), Marlon Byrd (face), Andrew Cashner (shoulder) and Matt Garza (elbow) on the DL.
DeWitt, who has never played the outfield in the big leagues until this year, went 3-for-4, including an RBI triple in the third in the Cubs' 12-7 loss to the Astros. He will get the bulk of playing time unless the Cubs tap into the farm system again.
"I'll give him a shot," Cubs manager Mike Quade said. "I know he slips and falls on the one ball, but he throws the guy out at the plate [in the seventh] and gets three hits. I'd like to keep his bat in the lineup. He's worked hard in left field. Why not?"
Quade said he could always insert a more experienced outfielder later in the game for DeWitt.
"At this point, we need his bat in the lineup," Quade said of DeWitt, who was hitting .280.
The Cubs have already called up outfielders Brad Snyder and Lou Montanez from Triple-A Iowa. Among the other options are Tyler Colvin, who began the year with the big league team but was sent down to Iowa after batting .113 in 28 games. He was hitting .260 in 12 games at Iowa with five doubles, two triples and one home run. Another choice may be Brett Jackson, the team's No. 1 Draft pick in 2009, who just rejoined Double-A Tennessee after being sidelined with a finger injury. Jackson was batting .295 in 32 games before he was hurt May 11.
Soriano was batting .271 and leading the Cubs with 12 home runs and 29 RBIs.
"[Injuries] are part of this game," DeWitt said. "It's a long year. Every team is going to battle through injuries. Good teams will push through it, and that's what we'll continue to do."