The midfielder arrived in east London over the summer and has been a revelation after scoring two goals and bagging six assists since joining.
His performances in open play have been excellent, but Ward-Prowse offers something truly unique in his superb set piece deliveries, an attribute not held by anyone else in the England squad.
With the Three Lions facing Australia and Italy over the next week, the 28-year-old could undoubtedly have made a difference and according to Nolan, the club were left stunned at his exclusion.
Speaking on talkSPORT Drive, Nolan said: "I speak to James a lot and I'm very much involved in the set pieces so we speak daily.
"I do that with the gaffer but James is a major part of it because I believe that we've got the best set piece taker in the world at our disposal so we've got to use him as much as we can.
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"I must admit and I said it last time, he's just got better and better in the last few weeks and you can only see from his assists, his goals, his creative play and everything else.
"I just really can't believe that he's not in that squad, I find it astounding really.
"He was gutted. He didn't hide from it, he was gutted that he wasn't in because he genuinely believed that he should have been in it and we believed that he should have been in it.
"But he won't sit and sulk. He will go out there and prove them wrong because that's the type of character he is. He's a great lad."