The two city rivals clash at Pirtek Stadium for the second time this season after the Sky Blues won the first game 1-0 at Alianz Stadium.
Grant, who has played in seven derbies, is emerging as one of the most consistent players in Graham Arnold's side.
He has started in all 14 league games so far.
In round three, Grant had the better of Castelen but the Surinam-born winger is now fully fit and at the top of his game, making and scoring goals freely.
Grant has no illusion about the task ahead but he will be ready for him once again.
"Castelen's whole game is dangerous," the 24-year-old said.
"He has speed, he is very good at dribbling and he is probably one of their most dangerous players and if I come up against him I will have to be on my toes to stop him from causing us too much damage."
So how do you handle such a tricky opponent?
"It all depends on the circumstances. If he's running at you at pace it's very difficult to win the ball back so you have to time your tackle correctly or keep up with him," he explained.
"On other occasions you might get the opportunity to be very close to him and not let him turn: that's when you try to make him play backwards."
The Grant-Castelen duel is shaping as one of the key battles of the derby and Sydney's chances of beating the Wanderers hinge largely on whether Grant can contain the livewire winger.
Grant has played 109 league games for Sydney since he made his debut in 2008-2009.
He is one of the most popular players among the fans and he said he could not see himself playing for any other club.
He has scored four goals in total but none of them have come against the Wanderers, admitting he would give anything to get on the scoresheet on Saturday.
"Scoring in a derby is definitely one of the biggest things you could do," he said.
"It would be top of the ladder for me in my career and if it happens to be the winner against your biggest rival ... well, there could be no bigger thing."
Grant is an attacking player and said he did not feel his positive instincts were curtailed by his defensive responsibilities.
"Yes, I do like to attack and get forward as much as possible but as a fullback you have to abide by tactics and structure," he said.
"This makes you approach things differently but that's fine by me."
Grant's reputation as a utility can be seen as a double-edged sword.
Coaches love to be able to avail themselves of players who can comfortably fit into several positions and Grant is always one of the first players Arnold picks in his starting line-up each week.
On the other hand utility players often find that they cannot specialise in one particular role because they are continuously being asked to take up other positions to suit the team's needs.
"In the past my versatility and not being able to cement one position could have been a bit of a hindrance," he explained.
"Nowadays I look at it in a positive way. I'm always in the coach's mind, I suppose, whether I'm playing right back or left back or in midfield.
"I know it's a cliche but I'm always happy to play anywhere as long as I get a run."
Grant's approach to football has also endeared him with his own teammates.
Skipper Alex Brosque, who has seen at first hand Grant's development into a fine footballer, has only good things to say about the kid from Canowindra, in country NSW.
"What does he bring to the team? In one word: reliability," Brosque said.
"I've seen Rhyan come fresh out of our youth team and even from a young age he always looked right at home in the first team.
"His technique, fitness and work rate are the reason he's been a very important player to Sydney over the years and his ability to play in just about any position on the field, and play well in every one of those positions, is why I believe he is the most reliable player the club's ever had.
"It's been enjoyable watching him develop and mature over the years because aside from what he brings on the pitch, amongst the boys he's a very funny guy and very good at bringing the boys together."