In the final hours of the window, it seemed the 23-year-old Ivorian was closing in on a loan deal with the Dutch club believed to include a buy option for the midfielder, signed by Celtic in a £2m deal from Israeli side Bnei Yehuda two years ago.
However, Soro remains in Glasgow, though the later closing of the transfer window in various countries mean that the largely out-of-favour player, and the club’s Greek keeper Vasilis Barkas who could be bracketed similarly, could exit Celtic Park in the coming weeks.
“With guys like Soro it’s about trying to help them and if they get opportunities elsewhere to try and facilitate that,” said Postecoglou, as he spoke to the press ahead of hosting Rangers at Parkhead.
“There was a complication with Holland because unfortunately he needed to have a work permit sorted for us to do a deal yesterday. That didn’t happen. But with him and a couple of others there are still markets open and he is training well and available.”
Loan deals that took Osaze Urhoghide to KV Oostende, who will have an option to buy the right-back only signed from Sheffield Wednesday last week, and resulted in Adam Montgomery joining Aberdeen for the rest of the season were the only outgoings on a day expected to produce more.
The Celtic manager, though, was content with the chance for valuable game-time that will now present itself for left-sided teenager Montgomery.
“It’s a great deal for him to go to Aberdeen, a great environment, a good football club, a good coach,” he said. “It was important for me that we got him out, so we still had some work to do and there were a couple of others we were hoping to do that didn’t quite materialise.”