Yes, in the full book McGinniss wrote about this in much more detail than can be found in the papers - which still do name him as being investigated or suspected of involvement to some degree. Another redditor on this post put this well: McGinniss is emotional and subjective but there is very little reason to believe he would have made any of this up. He was the only journalist close enough to the team who blew the whistle on all of the dealings primarily because he was disgusted by it and couldn’t believe the inner workings of how football in Italy truly worked. In the book, that player directly implicates Gravina in the ring, amongst several other things. It’s a very good read even ignoring any of this and I’d massively recommend it.
Keep reading mate it’s a fantastic read. One of my all time favourite books.