Ange Postecoglou has eased any expectations on Yuki Kobayashi as he insisted his trip to join the squad training in Portugal is "just an introduction".
The central defender will officially become a Celtic player next month when the January transfer window officially opens.
But he's already becoming acquainted with his team-mates and the Celtic backroom team having trained with the club abroad this week.
Kobayashi, 22, has agreed a five-year deal to join Celtic from J-League club Vissel Kobe.
He first joined up with Celtic on December 1 but will have to wait until January 1 until he can feature competitively for the club.
"It's still very early for him, it's just an introduction," Postecoglou told Celtic TV of Kobayashi's start to his time at Celtic.
"We've got a good three weeks before he is even available to play so it's just a matter of him getting to know the lads and how we train.
"As always, the boys have been really good...the environment to bringing the new guys in and making them feel comfortable.
"He gets the next few weeks to bring himself up to speed."
The trip to Portugal also allowed Postecoglou to give game time to players returning from injury or requiring more game time during the break.
And the Celtic boss name-dropped Carl Starfelt and Callum McGregor as two players to benefit from the bounce game against Rennes.
Confirming the pair came through the match unscathed, Postecoglou commented: "It was okay. There were some good bits and some not-so-good bits.
"Overall, it was a good positive week. We got some good minutes into some players who, Callum and Carl, haven't played a lot recently and they have all come through it well."
Upon signing for Celtic, Kobayashi said: "I am so excited to be joining Celtic and I am really looking forward to this wonderful opportunity.
"I will be giving everything to try and be successful with the Club.
"Right across the world, everyone knows what a special club Celtic is and it will be a real honour to wear this fantastic jersey.
“The work of Ange Postecoglou is also really well-known in Japan after he had such a great time in the J League, and as well as being part of Celtic I can’t wait to work with him as a coach and the great team of players he has already developed.
“I know that Celtic over so many years has such a brilliant track record of success and I now want to play my part in bringing more great moments to the Club and our fans.
"I would like to thank Vissel Kobe sincerely for all the support that has been given to me in the early part of my career and now I look forward to embracing this exciting new challenge with Celtic, one of the world’s great football clubs.”
