Scrum half star Arr, who turned 21 last weekend, has made 32 appearances for Warriors in his career but is set for only his fourth start against the Exiles.
Ruddock admits he is now 'excited' by the possible chance to see his young Warrior let loose in the league from the start and believes the time is now right for Arr to step up and take his chance to impress.
He said: "Jonny has done well in recent games and we are excited about this opportunity for him,
"We are disappointed to lose Ryan, but this is the sort of opportunity that Jonny has been waiting for where he should get a run of three or four games now.
"It will be very interesting to see how he goes, I'm very confident he will go well and it is just the right time in his career to get these games under his belt and get that confidence to really push on.
"If you look at just about every player that has gone onto become top quality, it is about getting that opportunity that will either make or break you.
"I'm very confident that it will make Jonny Arr into a very fine player. He has already proved he can play at this level, what he has got to do now is back it up and play high quality rugby week on and week out.
"He has to get into the flow of the team and I think this is the chance he has been craving and waiting for."