Journalist Pete O'Rourke said that midfielder Riley McGree was in advanced talks over a move to Celtic.
The 23-year-old was on the verge of linking up with fellow Australian Ange Postecoglou in Scotland before a deal fell through.
But O'Rourke admitted that the Glasgow giants were close to making him their fifth signing of the January window.
What's the latest news involving McGree?
Postecoglou has already made a strong start to the window, bringing in Japanese trio Daizen Maeda, Yosuke Ideguchi and Reo Hatate from the J League late last month, while Johnny Kenny signed from Sligo Rovers.
And according to the Daily Record, Celtic had appeared to have won the race to sign McGree, who scored two goals and laid on two assists in a loan spell for Birmingham in the first half of this season.
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The outlet reported that McGree had agreed a £3m deal with the Hoops, subject to international clearance, with Postecoglou putting some personal touches on the deal having coached McGree previously with the Australia national team. In fact, he actually handed the midfielder his first ever international call up.
However, just when the deal appeared to be progressing smoothly, Middlesbrough joined the race and are now the frontrunners to sign McGree, with the Celtic boss confirming that his side have missed out.
O'Rourke revealed exactly how close Celtic were to completing their fifth deal of the window.
What did O'Rourke say about McGree?
He told GIVEMESPORT: "Celtic were in advanced talks to sign McGree from Charlotte. McGree had a loan spell at Birmingham in the Championship this season and did very well for them."
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Why is McGree likely to choose Middlesbrough?
According to Teeside Live, the main reason as to why the Australian decided to reject Celtic and pick Middlesbrough was because of Chris Wilder. The 54-year-old did an incredible job with Sheffield United, taking them from League One to the top-half of the Premier League.
Furthermore, the former Blades manager is already making headway at the Riverside, with his Boro outfit already within one point of the top-six after collecting 16 points from their previous six matches.
Therefore, McGree has essentially seen the prospect of a season in the top-flight with Middlesbrough as more appealing than potentially playing in the Champions League with Celtic next term.News Now - Sport News