Carr has not impressed at right-back - his true position - and when Kevin Keegan played him at left-back recently there were groans from the Geordies when the team was read out.
Sure enough he was well out of his depth, running around like a headless chicken, and many believe Keegan should send him to pastures new.
But Duff insists his mate is up for the job.
Duff: "Stephen has been great. He only has until the summer until his contract expires, but as a friend and a player I'd love him to stay.
"I know he's had his injury problems at Newcastle, like I have, but he is a great person to have around and most of the players would agree with that.
"He has the experience we need at the moment.
"People criticise players for being injured, but he hasn't moaned about anything.
"He just works hard on things, like I do, and he will always give 100%."