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The loaning of players in professional sports is a unique trend only found in association football and in rugby league.

In the case of the former, these deals can be for a whole host of reasons, including giving a young player more game time to build up experience, sparing a more experienced member of your squad the hardships of sitting out games, or even operating a try-before-you-buy methodology with regard to future permanent signings.

Celtic have used the loan market to great effect in the past, with two of their biggest modern success stories in Jota and Cameron Carter-Vickers both being bought off the back of successful loan spells orchestrated by the club initially. The former went for £25 million, whilst the latter is a defensive mainstay in the current Celtic backline.

Staying on the subject of defenders, and Celtic are experiencing a fair amount of movement this summer in that area of the team, particularly in the central positions. Carter-Vickers’ regular defensive partner Carl Starfelt is set to move on to La Liga side Celta Vigo, meanwhile, Maik Nawrocki has joined the club from Legia Warsaw in his native Poland.

The latest reports circulating would also make you believe that Celtic are also edging ever closer to the signing of Sweden cap Gustaf Lagerbielke from Elfsborg, also a central defender, whilst Volendam’s Xavier Mbuyamba has also been linked.

With all of this movement and speculation, you could be forgiven for failing to remember a certain January signing who now looks so far out of the picture in this position. That player would be Yuki Kobayashi, the 23-year-old defender signed in the winter window from Vissel Kobe in the J1 League.

READ MORE: Maik Nawrocki's impressive Celtic competitive debut analysed

Signed for over £1 million, Kobayashi was brought in by former manager Ange Postecoglou, who faced him when he was in charge of Yokohama F Marinos in the defender’s homeland. Following his signing, the Australian said: “He’s a left-sided centre-back which is an important position in the context of how we play our football, and having someone left-footed there isn’t easy to find.

“He has a fair bit of experience at the age of 22 and we thought it was a great opportunity for us, the fact we can bring him in now and get him settled. He’s one that we expect to make more of an impact as the season goes on and not one we will throw in straight away, but that depends on his progress. I’m really pleased to have him and I’m sure he will be great for us.”

Postecoglou kept his word, and Kobayashi was carefully nursed into the team, making his debut against St Mirren at home in January, before making sporadic appearances over the next few months. However, he would be called upon by the manager following Carter-Vickers’ need for surgery on his knee, finishing his season as a result. Because of this, Kobayashi now had a clear run in the team to impress the manager ahead of the new campaign.

His first game in this run was against Hearts at Tynecastle. Although he and Starfelt kept a clean sheet, the Japanese defender looked shaky in possession and not up for the Edinburgh side's physical style of play, especially at Tynecastle. He would then play the full 90 minutes in the 3-0 defeat to Rangers at Ibrox, in what was an unforgiving afternoon for the young stand-in.

Physically bullied in the air by John Souttar for the home side’s second goal, Kobayashi’s performance garnered criticism from many, who did not impress on the day whatsoever. Indeed, he would be benched in favour of countryman Tomoki Iwata – apart from a 4-2 away loss to Hibernian in which he played the full 90 minutes – and was not named in the squad for both Trophy Day against Aberdeen and the Scottish Cup final against Inverness Caledonian Thistle. A damning statement from the departing Postecoglou, as there was no word or acknowledgement of an injury on Kobayashi’s part.

Circling back to the discussion of loan deals, perhaps Kobayashi’s best course of action is to secure a move away from the club, at least temporarily. As mentioned earlier, Celtic have benefitted greatly with regard to the loan system in terms of their own youth players, especially in sending their players to other teams in the Scottish Premiership.

Indeed, two of the best examples of players who came back better players following successful loan spells come in the shape of Norwegian defender Kristoffer Ajer and Scottish midfielder Ryan Christie, who now ply their trade in the English Premier League. Both players went out on loan to Kilmarnock and Aberdeen respectively - where they physically matured and were standouts on the pitch - before returning to their parent club as better players thanks to their experiences. On their return, they were ready to challenge for first team spots, which they managed to successfully achieve.

READ MORE: Rodgers provides Lagerbielke Celtic transfer update

Who is to say that the same cannot potentially happen to Kobayashi? It will be interesting to see where Kobayashi does end up, particularly due to the fact that he has changed agents, which indicates movement one way or another with regard to his future. If Celtic are serious about trying to rejuvenate the defender given his poor start to life at the club, then a loan move back to the J1 League should be out of the question. Much like Yosuke Ideguchi, a temporary move back to his homeland effectively spells the end of his Celtic career, so unless the club are keen to cut ties completely, then this should be avoided at all costs.

So, where do you send him? Do you chance your arm and hope that Hearts will accommodate another Japanese player alongside Yutaro Oda and new signing Kyosuke Tagawa, on a loan deal? Will Aberdeen want Kobayashi ahead of Liam Scales, who was at the club last season? Or do you send him to a team like St Mirren, St Johnstone, Ross County or Dundee, where he would have to adjust and adapt quickly to a team that traditionally has less of the ball during matches?

Regardless of where he ends up, it is quite clear that the chances of Kobayashi breaking into the first team ahead of both the established and new players respectively are painfully slim at the moment.