Long, whom the Athletics acquired from the Giants on Sunday in exchange for cash considerations, was added to the 26-man active roster Monday.
Though Long has a minor-league option remaining and posted a 9.90 ERA and 1.90 WHIP across 10 innings at Triple-A Sacramento, the Athletics will have him report to the big club right away rather than joining their top affiliate in Las Vegas. Long is expected to fill a multi-inning role out of the bullpen after the Athletics placed one of their other long relievers, Adrian Martinez (elbow), on the 15-day injured list in a corresponding move.