Teammates are often praising each other, nothing new there; you've seen what he wrote about Matri? Pretty average striker, but Pirlo thinks the world of him. Apart from that short passage in the book when he described one situation, I really don't recall any other player suggesting Marchisio to be a leader, and what we have seen on the pitch from him till now, indicates that he doesn't have it, mentally. He needs to be there more for his mates, show more consistency, be a focal point, when things become tough others look up and place their trust in captain to lead them through difficult moments. After seeing Conte, Del Piero and now Buffon as captains, Marchisio would be a terrible choice. I honestly hope that peeps are trolling when they bring up his name for that role, I know Hustini does.
