A knee injury played a part in scuppering Turnbull's chances of a move to Glasgow.
After the problem was discovered in the player's medical, Celtic tried to revise their offer to Motherwell, which the Fir Park club rejected.
In spite of this, Celtic thanked Motherwell for their conduct in the process.
A club statement read: "It is unfortunate that we were not able to proceed with the transfer of David to Celtic, having agreed a significant fee with Motherwell and reaching agreement with the player.
"It is regrettable that David will be out of action for a considerable length of time and, clearly, these circumstances are totally outwith the club's control. We did everything we could to find a solution.
"We would like to thank David and his representatives for the professionalism they have shown throughout. We also thank Motherwell FC for the way they have handled this process.
"We wish David all the very best with the operation and every success for the future."