Mercado was activated from the 7-day injured list Saturday.
Mercado failed to make an appearance during spring training due to a shoulder injury, but he looked sharp during his rehab assignment in April, posting a 1.23 ERA and 0.68 WHIP over 7.1 innings (five appearances). He looked a little shaky during his first appearance for Triple-A Lehigh Valley on Saturday, surrendering two runs on three walks while striking out one over two frames.