Duck egg on day 39

[LearnDucksAndChicks]

I have one duck egg in incubator which is on day 39, other eggs hatched on day 28. This is not a muscovy egg. I Don't find any bad smell or bad things on the egg. Air cell is growing very slowly day by day, as of today it looks like it may take some more days. What shall I do , shall I stop incubating it, or stop..

 

[sourland]

If there are other eggs in the incubator, I would discard this egg just in case it explodes. I doubt that it might be viable, but who knows.

 

[MGG]

I have one duck egg in incubator which is on day 39, other eggs hatched on day 28. This is not a muscovy egg. I Don't find any bad smell or bad things on the egg. Air cell is growing very slowly day by day, as of today it looks like it may take some more days. What shall I do , shall I stop incubating it, or stop..

I would say it's long dead.
Can you post a few good candling pics?

 

[LearnDucksAndChicks]

Thanks for the suggestions, I will discard the egg from incubator. Will try to take the candling picture before discard.