Watson, the 42nd overall pick in the 2013 Draft, was shifted across to the left after an injury to starter Jared Veldheer. However he has now picked up a knock meaning right tackle Khalif Barnes will start in his place.
"Unfortunately, we've got two guys hurt, so it's 'next man up,'" Barnes told reporters. "I've done this position before.
"It's been a little while but I'll get back on the bike and start riding again. It felt good. We're going to go out and play ball. No excuses. I felt good about it."
Oakland face the Indianapolis Colts in their opener on Sunday.