"My bags were packed — literally. But it turns out that in the business of football, 90% means nothing," he said in a column for The Players' Tribune.
He added: "One day, when it looked like the deal was done, I got a text from Xabi.
'Jona, let’s have a chat.'
"We went to the meeting room, and Xabi, he has this natural aura... it’s hard to even say what it is, but it’s in the way he speaks and looks you in the eye. Sincerity like that can be rare in football. You know what he did as a player, but it’s even more about how he treats you as a person. He commands absolute respect.
"We had quite a deep chat. I don’t want to go into the exact details of what he said, but I’d been at Leverkusen for nine years, and he knew exactly how much this club means to me. He began talking about the qualities I bring to the team, and the influence I had on my teammates, and I got the feeling that he really saw me as someone special."