The Steelmen have already knocked back the Hoops’ opening 250,000 offer for the Northern Irishman.
Brendan Rodgers is looking for cover between the sticks after losing Craig Gordon for up to three months with a knee injury.
But Press Association Sport understands Well chiefs would be looking for a sum closer to 750,000 to let the 29-year-old – who they signed from Hartlepool for just 10,000 in the summer – make the move to Parkhead.
Fir Park boss Robinson admits it would be a “nightmare scenario” to lose his number one just a day before the end of the transfer window.
But he also insists Carson will be going nowhere unless Celtic – who have also been linked with Liverpool’s third-choice stopper AdamBogdan – dramatically increase their bid.
He said: “I spoke to Brendan yesterday after he had the courtesy to ring me. We then passed it over to the money men, Alan Burrows and Peter Lawwell.
“They had a chat but realised our valuations were miles away from one another.
“That’s as far as it has gone at the minute. Trevor is a Motherwell player and will stay a Motherwell player until our valuations are met.
“He is very much committed to Motherwell. He has two-and-a-half years left on his contract and it’s 24 hours left until the close of the window, so people will be sold from this football club at the right price when we decide, not when others decide.
“It would certainly make things very difficult for me (if Celtic did meet Carson’s valuation). Player’s valuations go up and down depending on what point in the window you’re at because the closer you are to the end then the timescale to replace them becomes very difficult.
“So it would have to be a very good bid for us to let Trevor go.
“But yeah, it would be the nightmare scenario if we had to let him go now.
“However, we always have things that we can do. Whether you can do that in 24 hours remains to be seen and hopefully we won’t have to do that.”
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