The 49ers defensive tackle said after Tuesday's walk-through practice that he partially tore the upper portion of his right bicep muscle during a play in Sunday's win over the Houston Texans.
McDonald, who will not require protective gear beyond his routine elbow pad, said he expects to play this coming Sunday, in San Francisco's Week 6 matchup opposite the Arizona Cardinals. He added that he expects to practice as well.
"I'll know more as the week goes on," McDonald said of his level of strength.
The seven-year veteran had said on Sunday that he suffered his injury on his way to sacking Texans quarterback Matt Schaub on a 3rd-and-9 play early in the third quarter. Later in the same period, one of McDonald's replacements made a big play:
"He did what he was supposed to do on that play," McDonald said. "We have a saying that we're always happy for a teammates success. If that would have been me, I could have gotten that pick too."