Mmmm, yorkshire pudding au jus…
I just don’t think people would realize what you meant if you said jus by itself (unless context made it very clear). The phrase has become fixed as au jus.
If the grammar bothers me, I’d just figure out a way to get it to work with “with juice.” For example, “I need a some more in my cup au jus.”
(Very old) thread relocated from IMHO to Cafe Society. Beware that you may be responding to someone who is no longer on the board.
Somehow the rest of us (British, South African, probably others) manage…
I’m not going to check the whole thread to see if I posted this before (I probably did, if I was posting at the time). But it always bothered me that, when Carl’s Jr. was selling a roast beef sandwich, they would truck to the store boxes which contained “Au Jus”. I always thought it amusing to ask my spouse (who ran a CJ’s) how much with juice came in the morning delivery. 
Nice…but although jus is pretty traditional with roast beef and Yorkies, I was brought up to appreciate something with a bit more body. I can still hear my Grandma saying - as she mercilessly beat flour into the meat juices with a fork - “I don’t like wishy-washy gravy”.
Good lord but that woman made some astonishing Yorkshire puddings…