Reports suggest Koeman remains genuinely concerned about Timber, who has been dealing with a groin problem for some time.
For any international side, losing one important player is disruptive. Losing several, just before a major tournament, can force a manager into compromises he would rather avoid. Timber is valuable not only for his defending, but for his calmness in buildup and his flexibility across the back line.
If Timber is the concern, Memphis Depay appears to be the brighter storyline. Reports suggest Koeman is more optimistic that the forward can rebuild rhythm in time after his own injury setback.
That is a crucial distinction in tournament football. A returning forward can be available on paper and still be a long way from decisive.
The reported opener against Japan already looked awkward on paper. Now it appears to be carrying even more weight. If Depay regains momentum and Timber makes it, the Dutch outlook changes quickly. If not, the next storyline to watch is whether Koeman trims expectations or finds a new shape before the tournament truly begins.