Semien, whose procedure involved repairing a fracture to the scaphoid bone, is eligible to come off the 60-day disabled list June 14, but he still has several steps ahead of him before rejoining the A's.
His latest progress was highly encouraging, nonetheless, as the A's anticipate the return of their everyday shortstop, an ironman of sorts for them the last two seasons.
"It'll take some time," Melvin said. "We're going to have to go through multiple days of [throwing], he's going to have to start swinging the bat, and at some point he's going to go out on a rehab, so we're not close as far as putting together a timetable for him, but the fact that he is playing catch is significant.