But the way offensive line coach Mike Tice sees things, Penn holding out may be a blessing in disguise.
"Well it's always good when you develop in depth," Tice said after practice on Wednesday. "We had a number of days when we were down to 11 and 10 players."
Tice referenced rookie tackle David Sharpe getting banged up and missing "five or six" days," rookie tackle Jylan Ware suffering a concussion and All-Pro left guard Kelechi Osemele "practicing every other day" in camp.
"When you have that, you get the ability ... the opportunity to develop your depth. In the long run, it's actually a good thing."
What about when Penn ultimately returns and regains his left tackle spot?
"Where I'm at right now is I have to get us ready to go out and beat Tennessee," Tice said of the Raiders' season opener on Sept. 10 in Nashville. "So right now, I have Marshall on the left and I have Vadal on the right and I have David doing a little bit more each day, playing both sides. That's what we have.
"I can't sit here and wonder when D.P. is going to come back. Right now I've moved forward with Marshall is on the left and Vadal is on the right and David is swinging. That's reality right now. I can't think that there's going to be something else there until it's there."