David Turnbull's move from Motherwell to Celtic could be off after an issue emerged during the player's medical.
Last week, the Steelmen accepted an offer of £3m from the Premiership champions for the talented teenager.
English side Norwich City also had a bid accepted after Celtic appeared to pull out of the deal.
But, after a u-turn, the 19-year-old midfielder returned to Glasgow and agreed personal terms with the Hoops and was set to be Neil Lennon's first signing since his return to the club.
However, after a medical the move appears to have hit another bump on the road.
Following this latest development, in light of his medical, the two clubs are in discussions with how best to deal with the situation going forward.
Meanwhile, Celtic have leapt to Lurgan native Lennon's defence after the Parkhead boss was criticised by West Brom over his treatment of Oliver Burke.
The Scotland international was signed on loan by Brendan Rodgers in January but Baggies technical director Luke Dowling was left furious with the way the 22-year-old was handled once Lennon took over in February.
Dowling refused to go into the specifics of his complaint, but he strongly insisted there was no chance the £15m attacker would be heading back to Glasgow while Lennon remains in charge of the Hoops.
"Olly Burke will not be going anywhere near Celtic with the current manager," he said.
However, those comments drew a sharp response from the Hoops.
In a statement, the Scottish champions said: "These comments, which question the professionalism of both Neil and Celtic Football Club, are ridiculous and completely inaccurate.
"West Brom have made no contact whatsoever with either Neil or the club in relation to Oliver.
"As with every player who comes to Celtic, Oliver received the very best of treatment and every support and opportunity. We wish Oliver the very best for the future."
Dowling launched his broadside on Monday as new Baggies boss Slaven Bilic was unveiled at the Hawthorns.