Top Astros pitching prospect Mark Appel felt pain overnight Wednesday to Thursday and went to a Houston hospital, where a standard appendectomy was performed without complication.

“It was kind of a routine emergency,” general manager Jeff Luhnow said.

Appel, 22, shouldn’t miss much of spring training, if any.

“Mark will be fine,” Luhnow said. “He will report to camp on time. Once he arrives in Spring Training, we’ll see where he is at health-wise and take it from there. We anticipate that he will either be ready to work out at the start of camp or very close to ready.”

The typical recovery time in baseball for an appendectomy is two to four weeks. The top pick in last year’s amateur draft, Appel has been invited to major league spring training. The righthander is not expected to make the team out of camp, but he also is not far away.

Another Astros pitcher also underwent surgery Thursday in Houston, southpaw Raul Valdes. Unlike Appel, Valdes is expected to miss a significant portion of spring training, potentially more than half of it. The expected recovery time from the arthroscopic procedure performed on Valdes’ left knee is 4-6 weeks.

Luhnow said Valdes suffered the lateral tear to his meniscus in late December while playing winter ball in the Dominican Republic. The team wanted to examine Valdes here in Houston, contributing to the time in between the injury and the operation.

Valdes was claimed off waivers on Oct. 2 from the Phillies. The 36-year-old from Havana was expected to compete for left-handed bullpen jobs with Kevin Chapman and Darin Downs — who now may have an inside track with one less competitor for half of camp.

Appel and Valdes join righty reliever Jesse Crain on the list of Astros who potentially won’t be ready for the start of spring training. Appel and Valdes join righty reliever Jesse Crain on the list of Astros who potentially won’t be ready for the start of spring training. Crain, a free-agent signing, is recovering from right biceps surgery.

Crain is slated to attempt to throw for the first time on Monday. He believe he’s only a few weeks behind.