Mr. M, does your engine use oil? If it does use oil, could be from valve guides or rings. Run a compression test, if that checks out & you don't use oil, don't worry about it.
However if your engine consumes oil & the compression checks ok, it still could be valve guides or the rings did not seat in that cylinder.
Advise need more history on your engine. Such as how much oil your engine is using, if no oil consumption I would not worry at all. William