SAN FRANCISCO — San Diego Padres left-hander Shawn Estes broke the thumb on his throwing hand when he fell on the tunnel stairs between the team's clubhouse and dugout last night.

The Padres placed the pitcher on the 15-day disabled list today after X-rays late yesterday revealed the broken bone, a discouraging development for a player who was on his way back. The 35-year-old Estes was scheduled to start Monday back home at Petco Park in the series opener with the Chicago Cubs.

"I just landed on it wrong," Estes said. "I thought it was a little sprain at first. I'm hoping that's the extent of it and there's no tendon or ligament damage, or it would take longer. ... I just fell. I put my hand down to catch myself and my body weight came down on it to catch my fall."

He was coming down the stairs between the sixth and seventh innings against the San Francisco Giants, his former team.

Estes, who didn't pitch in the majors last year while recovering from Tommy John surgery, is scheduled to be examined by a hand specialist Monday in San Diego to determine whether he might need surgery to have a pin inserted into the thumb or if it can heal on its own.

Estes was called up from Triple-A Portland on May 8 after going 4-2 with a 3.67 ERA in six starts at that level, then that night at Atlanta made his first major league appearance since April 5, 2006.

Estes was 7-8 with a 4.80 ERA in 21 starts for Arizona in 2005.

"I feel like I'm going to wake up from a dream," Estes said. "I've been through a lot the last couple of years. It's very disappointing, borderline depressing. I'm going to stay as far away from the Golden Gate (Bridge) as I can the next couple of days."

The thumb quickly became very painful and then went numb. When Estes tried moving it to test his motion, it began turning blue from all the blood. He waited a half-inning to tell the Padres' medical staff, then Giants team orthopedist Ken Akizuki performed an X-ray.

"I was thinking, 'This is kind of embarrassing to say,"' Estes said. "I didn't want to believe it at first."

San Diego hasn't said who will start in Estes' place Monday, but right-hander Cha Seung Baek is an option. He struck out the side in the 12th on the way to the win in the Padres' 7-3, 13-inning victory Friday night.

The club called up right-handed reliever Carlos Guevara from Portland to take Estes' roster spot. Guevara missed much of spring training with groin and hamstring injuries.