Nah, think we can safely rule out him moving to Celtic. He has his eyes on bigger things which means we can also rule out him playing in the championship... http://www.insidefutbol.com/2015/06/08/john-guidetti-blasts-celtic-boss-ronny-deila-said-different-things-to-me-than-in-public/213345/
Guiddetti could be lethal at Championship level and as he scored 23 goals in 20 appearances for Feyenoord shows he knows where the net is, but yeah his attitude def needs sorting.
There's a few on that list who could be good additions, players like Ross Wallace, Chris Herd, Maynor Figueroa...