Mullan is currently trialling at Carlisle United and caretaker boss Greg Abbott said: "He handles the ball really well, he's got good delivery and he's got that yard of pace.
"He's an old-fashioned winger, a Jimmy Johnstone type of winger, and hopefully he can do well for us.
Abbott also revealed: "I've known about Jamie from my Leeds days, because Leeds were trying to sign him at the time Man Utd took him from Notts County.
"He was highly-rated as a young player.
"At Man United it takes a hell of an effort to get right the way through.
Now he's trying to take a step back to kick his career forward again.
"We're willing to give him that opportunity and there's no time limit with it. I don't like rushing things with trialists if we don't have to.
"He trained on Friday, he stayed up to watch the game on Saturday and now he's in for the full week at least. He knows Joe Garner from England under 18 games, so Joe is looking after him.
"He looked really bright and sharp on Friday. I think he favours the right wing but he looks to come inside from the left as well, and it probably helps his situation if he can do both."