What about Messi?

Today I was reading my magazine and looking at the transfer rumours as I usually do and then I saw a shocking one and I looked it up and according from Caught off side and Match the mag Manchester City are preparing a record bid for World super star Lionel Messi of £150million! From my sources this story might be true and Manchester City haven't spent big money yet because they are saving up for him.
Barcelona might consider it as they are in a lot of debt and that money could be helpful but who would they sign to replace him? Messi has scored 169 goals and still counting in 345 games. He has just turned 25. But in his contract his  buy out Claus is £250million. Messi joined Barcelona when he was nine because he needed health care because he was so small. And many clubs offed him that but Barcelona won the race for him and he was in their academy.
Messi in the last two seasons has scored of thirty goals in the league and last year he scored fifty goals in all competions in as you say a disappointing season only winning the Copa Del Rey. But could Barcelona sell the best player in the world?