Donald, 10th in the world, did himself no favours by missing the USPGA cut
Martin Kaymer's USPGA win and Rory McIlroy's joint-third finish did little to ease European Ryder Cup captain Colin Montgomerie's team selection.
Kaymer, McIlroy and US Open champion Graeme McDowell are certainties to feature at Celtic Manor on 1 October.
But Lee Westwood (ruptured calf muscle) and Ian Poulter (chest complaint) are slight doubts, and some star names look to be relying on wildcard picks.
Paul Casey, Justin Rose, Luke Donald and Padraig Harrington are among them.
England's Ross Fisher and Italian Francesco Molinari are close to making sure of their appearances at Celtic Manor in south Wales, but the battle for the remaining two automatic spots and three wildcards looks increasingly complicated.
Miguel Angel Jimenez and Casey, thanks to his 12th place at Whistling Straits, are eighth and ninth on the table, but Casey has decided not to play the race-ending Johnnie Walker Championship at Gleneagles in two weeks and cannot therefore add to his total.
Harrington is less than 1,000 points behind him in the European points list but neither is due to play any more ranking events as both are keen to play in the FedEx Cup play-offs in the United States which do not count.
The same scenario applies to US Tour winner Justin Rose. There is little point in him returning because he is too far back on the European points list.
Donald is ranked 10th in the world but he missed the cut in Wisconsin along with Rose and Harrington, and all three appear to be relying on Montgomerie's generosity.
But Casey and Molinari's brother Edoardo appear to be in much better form than them and Montgomerie may feel they are more deserving of Ryder Cup selection should they miss out on automatic berths.
Two years ago Poulter was heavily criticised for not returning to Europe to qualify, though when picked by Nick Faldo he proved to be the best player on the team.
1 LEE WESTWOOD 422.0
2 RORY McILROY 316.9
3 MARTIN KAYMER 285.4
4 GRAEME McDOWELL 249.3
5 Luke Donald 231.1
6 Edoardo Molinari 218.4
7 Ian Poulter 211.2
8 Padraig Harrington 204.9
9 Justin Rose 195.7
10 Francesco Molinari 172.5
1 Lee Westwood 3,446,137
2 Martin Kaymer 2,638,282
3 Rory McIlroy 2,368,205
4 Graeme McDowell 2,307,041
5 IAN POULTER 2,238,874
6 ROSS FISHER 1,708,614
7 FRANCESCO MOLINARI 1,612,747
8 MIGUEL ANGEL JIMENEZ 1,499,775
9 PAUL CASEY 1,487,776
10 Padraig Harrington 1,486,529
Capitals denote players in qualifying positions. Top four on world list qualify, plus top five on European list not already qualified. Montgomerie has three wildcard picks in addition.