Mattingly said he only had the "layman's" explanation, but said a worst-case scenario would mean Blake could be out four weeks because doctors might need to "open up and flush it out, and there's a period of time for that.
"We've got to be careful with what we do," the manager said. "You can't play around with it. We have to make sure we take care of it properly."
Blake, 37, started the season on the DL with an inflamed thoracic disk, missing the first six games of the season. But he's hit .321 in 14 games since returning.
"I can't even explain it," Blake said when asked if the latest setback was frustrating. "It's such a bizarre start of the season. I feel I've let my teammates down. I'm not with them. And we were playing good, too."
He missed a game Monday with a tight groin, and the elbow started to swell Monday night. Blake said he has no idea what he did to cause the elbow to swell.
"I'm sure he's disappointed," Mattingly said. "He had the injury this spring, came back, then the groin thing. The elbow looks like something more of a long-term thing. It's frustrating for us. He looked like he would be at full strength. But we've got to be cautious. Stan [Conte, trainer] is talking more like four weeks. It's more than a 15-day DL."
Mattingly said the most likely callup would be infielder Russell Mitchell, who is off to a very slow start at Triple-A Albuquerque, but "he's been swinging the bat the last week. He's a guy that plays the position [third base]. He'd probably be the first thought. It could be other guys too."
If Juan Uribe was healthy, the Dodgers wouldn't be limited to calling up someone with third base experience, but Uribe hasn't started in five games. Aaron Miles started his third consecutive game at third on Wednesday.