No Bumgarner surgery

Eight days after his dirt-bike accident in Colorado, lefthander Madison Bumgarner began a prolonged rehabilitation on Friday that will extend past midseason.

The Giants’ ace was diagnosed with a Grade 2 sprain in the AC joint of his throwing shoulder and will be shelved until soon after the All-Star break, according to head athletic trainer Dave Groeschner.

Groeschner confirmed Bumgarner won’t need surgery, which wasn’t a surprise. The trainer said Monday that surgery was unlikely, and several doctors — including Giants orthopedist Dr. Ken Akizuki, who consulted with 49ers doctor Tim McAdams — agreed rehabilitation is the proper route.

At first, the Giants weren’t certain whether the sprain was Grade 1 or Grade 2, which is more serious and involves slight ligament tears, with the collarbone partially out of alignment.

A Grade 1 sprain is a mild shoulder separation with no collarbone movement.

Bumgarner was hurt April 20 on the Giants’ off day in Denver. He said this week he expects he will pitch again this season: “I would certainly be disappointed if I wasn’t.”

He’s on the disabled list for the first time in his career. His rehab is being overseen by Tony Reale, the Giants’ physical therapist. Briefly: Shortstop Brandon Crawford had an MRI exam shortly before the game to determine the extent of his groin injury. Crawford’s threeday bereavement leave ended Friday, and the Giants must activate him or put him on the disabled list before Saturday’s game. He returned after attending funeral services for his wife’s sister . ... With the MRI exam on Denard Span (sprained sternoclavicular joint) coming back clean, he can engage in baseball activities. John Shea is The San Francisco Chronicle’s national baseball writer.