Barrie, welcome to the GWF. I can't find much about this battle. It isn't mentioned in either edition of Under The Devil's Eye
and is only given a couple of sentences in The Gardeners of Salonika
, which says "The British, for example, had fought two sharp engagements, one on the Vardar and the other across the Struma. In the first, five infantry battalions had come up against a German regiment dug in to well planned positions on the crest of a hill overlooking the village of Machukovo; and had lost almost half their effective strength, without dislodging the Germans."
The village, like many others, was already in ruins from the Balkan wars that immediately preceded WW1 and lay just to the east of the river Vardar between the two front lines. It's on this map
. The country up there is a series of rolling, limestone hills that were a nightmare to attack.
There were Turks among the Central Powers troops in this theatre but they were few and far between - and only on the Struma front I think - so it's very unlikely that they had anything to do with his death. He was almost certainly killed by a German or, possibly, a Bulgarian soldier.