Veldheer will miss the entire season with a triceps injury, leaving Watson and Alex Barron the contenders to replace him protecting the blindside.
"Obviously that's something you've got to consider," Allen told the San Francisco Chronicle.
"But again, when you look at where we took this guy and you look at the roster and you look at his potential, I feel like that's the right thing to do.
Put him over there and see how he does in the game. We won't know until we put him in a game and get a chance to evaluate him. We haven't had that opportunity yet."
Oakland begin their regular season campaign against the Indianapolis Colts on September 8.