Elevated to vice-captain this season, Scully has again found himself in the spotlight after three lacklustre displays to start the year.
The midfielder, who turns 22 next month, has averaged just over 15 disposals in Greater Western Sydney's three losses, including just 11 against St Kilda in last week's 72-point defeat.
It led one television program to break down what each Scully possession had been worth in relation to the multi-million dollar contract he signed when joining the Giants at the end of the 2011 season.
It hasn't been the performance expected of a marquee signing at a new franchise desperate for big names, but Sheedy insists Scully will prove the critics wrong.
"He's a player that's going to take a while to be a good player," Sheedy said.
"What happens is, you sign up a young player and you think they're going to be a superstar straight away and it doesn't happen.
"It takes a long time in this game to be a real, top-class player. Sometimes it might take 50-to-100 games.
"Go back and look at (Tom) Hawkins. Geelong were probably nearly going to say, 'Look, I think we'll move on and go for someone else,' and then he pulls a game out in the Grand Final and wins a premiership for them.
"You never know with players how long (it might take)."
Asked directly if he can still be a superstar, Sheedy confidently said yes "because he's a running machine", comparing him with Richmond's games record-holder Kevin Bartlett.
"Kevin Bartlett had a great engine. He ran and kicked goals, but in his early years he kicked points," Sheedy said.
"(Scully's) got as big an engine as Kevin Bartlett. Kevin Bartlett at the same age would be a better player than Tom, but in the first three years of Bartlett's career, we were all still hoping he would be a good player.
"It takes a while to be an excellent player in the AFL."
One player who will make a welcome return to the GWS side this week is Irishman Setanta O'hAilpin.
Replacing Jon Patton, it will only be O'hAilpin's second match for the club after rupturing his ACL on debut in round six last year.
He also may need to help out in the ruck due to Dean Brogan's suspension.
Andrew Phillips and Tom Downie are the other developing GWS ruckmen behind Jonathan Giles, but Sheedy says bringing in a big-name ruck option is a key focus for next season.
"We'll be looking at a top-class ruckman somewhere and we've obviously got enough draft picks that we can share around with the trading that we've done," Sheedy said.
"We'll trade for an A-grade ruckman."
Sheedy said he will make between 4-6 changes this week to take on a Melbourne outfit also languishing at the foot of the ladder – and he knows victory won't be easy.
"Go and ask Carlton. Go and ask North Melbourne. They haven't won a game yet," he said.
"It's probably a final for both clubs trying to get into the top of the bottom four at the moment.
"We have to be at our best."
James Dampney is a reporter for AFL.com.au. Follow him on Twitter: @AFL_JD
