According to Roch:
"In case you missed it, the Orioles put Javy Lopez on the disabled list today and activated Luis Matos. Lopez's move is retroactive to April 28. He's suffering from what the club is calling a "mid-back strain."
Matos was 3-for-9 with a homer and two RBIs in two injury rehab games at Single-A Frederick. He joined the Orioles in Boston."