PHILADELPHIA — Boston Red Sox pitcher Bartolo Colon was placed on the 15-day disabled list today with a stiff lower back, and injured right-hander Curt Schilling was sent back to Boston for an examination with team doctors.

Boston recalled righty Chris Smith from Triple-A Pawtucket to take Colon's spot.

Colon (4-2, 4.09 ERA) was injured yesterday taking a swing during an at-bat against Phillies starter Cole Hamels. Colon left after five innings because of the stiffness.

"He has a history of issues, that's why we're being somewhat cautious," manager Terry Francona said before the Red Sox played the Phillies. "We would like to have him for the whole year and not just have him, but have him be productive and healthy."

Schilling, on the 60-day DL since spring training with shoulder weakness, will head back to Boston to have his shoulder examined by medical director Dr. Thomas Gill. Francona said Schilling had reached a "little bit a plateau" in his recovery.

"It's been a frustrating week for him," Francona said.

Francona said Daisuke Matsuzaka was set to start Saturday against St. Louis. Matsuzaka (8-0, 2.53 ERA) allowed two runs and three hits over five innings in a rehab start for Triple-A Pawtucket on Monday night, his first game action since straining his rotator cuff last month.

Also, first baseman Kevin Youkilis didn't start for the second straight game because of muscle spasms in the middle of his back. Youkilis said he felt tight and hoped to be ready for Wednesday. But Francona said he might rest Youkilis one more day, especially with the Red Sox off on Thursday.