Arians said after a practice session in Sarasota, Fla., the tip of Johnson's finger was ripped off during the Cardinals' 31-7 loss to the New Orleans Saints Sunday, The Arizona Republic reported.
The injury apparently happened when Johnson tried to get around a block while defending on a punt.
The newspaper said Johnson is expected to return this season, perhaps as early as Sunday, after the finger was repaired by shaving the bone and covering it with skin.
The safety said he saw blood leaking from his glove but believed it was a torn nail until the glove was cut off and his fingertip stayed inside.
"I'm not even sure how it happened," he told the Republic. "If I had to take a guess, I would say maybe it dug into the turf there and snapped back and broke it that way. My glove was torn or ripped, which makes me think it didn't get caught in a facemask or a cleat stepped on it."