The Partick Thistle keeper hoped the knock to Fox, which has left him facing eight weeks on the sidelines with a thigh tear, would allow him to stake his claim as the Jags No.1.
But he has seen his dreams of regular first-team action dashed after hurting a knee in the build-up to the Jags' 1-0 defeat to Hamilton Accies on Friday night, when new arrival Graeme Smith was thrust into action.
The ex-Well keeper then went on to endure a debut to forget as he allowed Ali Crawford to score directly from a corner but, unfortunately for Scully, he is unable to put in a challenge for a starting place ahead of this weekend's Irn-Bru First Division clash at home to Livingston.
He said: "It is frustrating, especially with this being my last year because I want to be playing games so I can try to impress the manager to win another contract.
"The gaffer explained his thinking to me and I just need to keep on working hard. He was good with me, he talked me through the decision and said that I had a big future in the game if I kept working hard.
"I will get my chance. I have had a few niggling injuries this season but I know I need to keep going and trying to impress the manager.
"I try to leave the contract stuff out my head, Hinchy [Craig Hinchcliffe, Thistle's keeper coach] is good with me like that and he keeps me working hard and focused.
"It is an injury I have had since the start of the season and unfortunately during the warm-up on Friday I went over on my knee.
"It is a weakness I have got there and it could be a couple of weeks before I am back. I'll do some strengthening work on it and hopefully I can get back a bit earlier.
"Not being able to play is the worst thing about it. I just need to keep my head down and hopefully I will get my chance again.
"I need to play as many games as I can at this stage of my career to aid my development so hopefully I will be back sooner rather than later."
With Jags manager Jackie McNamara placing his faith in Smith to star as his stand-in keeper while Fox battles back to full fitness, Scully may have to enjoy action away from the first team in order to prove his worth.
He has been a regular in the reserves this term and the 20-year-old admits the match action has been welcome.
He said: "Playing in the reserve games does allow you to keep your match fitness up. We have a league this season which means you are getting games every week, and that does help a lot.
"In the past, it was just the odd game here and there but it is more structured now.
"You can try things in those games.
"You want to keep your standards high and playing every week in these games helps to do that."