The newspaper claims Celtic will pay £2.8 million up front, with a further £400,000 due in add-ons.
But Well are said to be chasing further compensation, in the shape of either Mikey Johnston or Lewis Morgan on a temporary transfer.
Neither, though, are naturals in Turnbull's favoured central midfield role, and are perhaps more likely to fill the left-or-right-wing position recently vacated by the Rangers-bound Jake Hastie.
Hastie has signed for Celtic's main rivals ahead of his Motherwell deal expiring, although it has been claimed that he, too, could be on his way out of Glasgow on loan.
Johnston enjoyed his best season yet for the Bhoys, scoring or making six goals in 23 outings.
Morgan's wasn't quite so successful, however, ending with his loan club, Sunderland, defeated in the League One play-off final.
Which of Celtic's young pair would you like to see loaned to Motherwell?
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