I'd be more surprised if there wasn't a release clause given his career moves to date.
Plus we have said and shown that we never keep a player from moving on if a suitable deal is there to be had anyway.
If we can split the £51m fee over a few seasons, which apparently we will be doing, and can command at least £150m+ after two or three seasons then I'm OK with that worst case scenario. As will our financial statements.
For me the frustrating thing would be if it kicks in after 2 years. Even Dortmund got 2 & a half, would have expected any clause not to be active until after 3 seasons.