I hadn't considered the lucky-loser situation. I'd be interested to know the average number of LL's in grand slam tournaments, as it's now not just injuries to consider but possible positive covid tests. I wonder what happens if they run out of LL's - walkovers in the first round?
It is quite a different problem from USO and FO...
In both of those, virus was spreading widely in the cities and lots of people (taxi drivers, cleaning ladies...) that come home every night can give the virus to players.
Here in Victoria, virus is super low, so contamination just can come from abroad with players and their staff or officials.
It is far less people to check and if tested every two days, with low contact occurence (same players training together) and controlled movement (5 hours out of hotel room).... they should not find any case after 2 weeks or at least 3 weeks for those initially positive.
So we should not have a galore of LL because of COVID tests.
That said we can have players in relative doubtfull shape hoping to improve/recover during quarantine and Pre Event and realizing they do not at the very late moment or of course late injuries....
First time the field (including qualifiers) is frozen one month before the tournament.