The Swede's protracted season-long loan deal from Manchester City was belatedly confirmed last night after FIFA granted Celtic special dispensation to sign the 22 year-old, despite some of the paperwork relating to the move not being concluded until after the transfer deadline.
"After checking the documentation received and the information contained in the international transfer matching system managed by FIFA TMS, the Scottish Football Association was informed today that the envisaged loan deal may proceed," read a typically dry FIFA statement.
Celtic will find out next weekend if it has been worth all the hassle. In interviews Guidetti, currently on under-21 duty with Sweden, comes across as a fascinating character, bursting with self-confidence.
A City player since 2008, this is the fifth time he has been farmed out on loan, the previous four delivering varying levels of success. It was at Feyenoord in 2011/12 that he really came to life, scoring 20 goals in 23 games. a campaign that included three hat tricks. That earned him the adoration of the Feyenoord fans and had some tipping him to start for Sweden in Euro 2012 alongside Zlatan Ibrahimovic.
At his 20th birthday party in April of that year, however, things took a turn for the worse. A mystery stomach virus sustained that night started to attack his nervous system, effectively paralysing his right leg. He barely kicked a ball for the best part of the next two years. When he returned in January this year, it was at Stoke City on another loan spell.
The feeling was this would be his chance to recapture the highs experienced during his year in the Netherlands but instead it proved to be something of a comedown. He played just six times for Mark Hughes' side, all as a substitute, and failed to register a goal.
His self-belief, however, remains undiminished. In an interview carried out shortly after joining Stoke, he told of his plan to open a flower shop when he finally hangs up his boots, and send bouquets to all those who said he would never make it. "We'd call it Flowers for Doubters and send flowers to all the people who doubted me," he said. "All those people, they don't realise they drive me on. The flowers would be a little thank you."
For one so young, he has led a colourful life. It has included two stints living in Kenya as a child, a place he describes as "my favourite place on earth". He intends to live there when he retires and has established the John Guidetti Foundation to help build football pitches and schools. He has one full international cap to his name but ambitions to do so much more.
The comparisons with Zlatan are inevitable and, like his compatriot, he has no problem outlining his vision for the future. Unsurprisingly, such a talkative approach is sometimes divisive. "I speak my mind. I go to Holland and say I'm going to score 20 goals. And I do it. You get injured for two years and you see people saying: 'He's nothing.' That's Flowers for Doubters, man. The people who say you can't make it - you're going to eat your words."
Whether Celtic have signed the Guidetti who sparkled at Feyenoord or the one who struggled at Stoke remains to be seen. The player, though, is evidently happy to be given the opportunity to play for the Scottish champions, even if there is still doubt over whether he will be eligible for the Europa League campaign. "Delighted to have finally joined @celticfc on loan . . . Can't wait to get started and play in front those fans #TheBhoys," he tweeted.
He could make his debut against Aberdeen at Celtic Park a week tomorrow. It is unlikely to be dull.