The 27-year-old has been diagnosed with bursitis, an inflammation of the prepatellar bursa at the front of the knee. He has been dealing with it for most of the season but recently had it flare up while catching left-hander J.A. Happ in the bullpen.
"It's been there for awhile," Arencibia said. "We tried to take care of it before the All-Star break, and it started getting a little bit better, but bursitis, the recipe for that is rest, and there's no time for that."
Arencibia said the pain is most noticeable when he is attempting to block balls in the dirt. The ailment is expected to linger throughout the remainder of the season.
Backup catcher Josh Thole was in the starting lineup on Friday, making his fourth consecutive start behind the plate, and he went 1-for-3 with a walk. Thole will continue to carry the load until Arencibia returns, which could happen either Saturday or Sunday. Veteran utility man Mark DeRosa is also available to catch should the need arise.
Following a hot start, Arencibia has struggled at the plate. He is batting .211 with 17 homers, 45 RBIs and a .641 OPS, but dismissed any notion that his injury could be related to his offensive woes.
"I don't think so, I'm not going to sit here and say those things," Arencibia said. "It's bothered me before, it'll take me a while to get loose. I've definitely felt it throughout different parts of my game, but I think it's something that is a nagging injury. You can't really do much other than rest. It's there."
Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, and follow him on Twitter @gregorMLB. This story was not subject to the approval of Major League Baseball or its clubs.