Mercedes are potentially facing a challenge to their supremacy at the Austrian GP after Ferrari set the pace and Nico Rosberg was pitched into a crash by a suspension failure in Practice Three.
After dominating Friday, Mercedes experienced a fraught final build-up to Saturday's later qualifying session as Sebastian Vettel and Kimi Raikkonen unexpectedly set the pace for Ferrari.
Most pressing among them is the cause of Rosberg's heavy shunt and whether they will be able to repair the world championship leader's car in time to take part in qualifying, which begins at 1pm BST.
Mercedes have already confirmed the German will take a five-place grid penalty for a gearbox change.
Exiting Turn Two at the start of a fast lap, something appeared to break on Rosberg's left-rear suspension as he went over the kerb, with the W07 snapping straight left into the barriers.
Rosberg was unharmed and on his return to the garage was seen shaking his head in apparent anger at the accident, which did substantial damage to his car.
The German had been Mercedes' lead runner on Friday and Lewis Hamilton was unable to outpace the Ferraris when the session restarted after the red flag, finishing 0.210s back on the them in third place.
In a further potential complication for Sunday's race, Mercedes had earlier experienced rear blistering on the ultrasoft tyres on heavy fuel, with Hamilton's problems particularly pronounced.
Ferrari have introduced an upgraded engine for this weekend's race and their one-two result will give them encouragement that they can challenge Mercedes for the front row. Vettel's pacesetting time of 1:07.098 is a new Red Bull Ring record.
The caveat for Vettel is that he already knows he will not start on pole on Sunday as he will take a five-place grid penalty for a gearbox change.
Home team Red Bull were again the third-quickest team in P3, with Daniel Ricciardo a tenth quicker than team-mate Max Verstappen.
Williams were close behind in sixth and seventh places ahead of Force India's Nico Hulkenberg, as McLaren showed encouraging from to finish with both their cars in the top 10. However, Fernando Alonso appeared to damage to floor of his MP4-31 when he ran wide at a penultimate corner which caught numerous drivers out during the session.
"What a messy session this has been for so many drivers, for so many different reasons," observed Sky F1's Anthony Davidson.
Practice Three timesheet
1. Sebastian Vettel, Ferrari, 1:07.098
2. Kimi Raikkonen, Ferrari, 1:07.234
3. Lewis Hamilton, Mercedes, 1:07.308
4. Daniel Ricciardo, Red Bull, 1:07.639
5. Max Verstappen, Red Bull, 1:07.761
6. Valtteri Bottas, Williams, 1:07.814
7. Felipe Massa, Williams, 1:07.831
8. Nico Hulkenberg, Force India, 1:08.285
9. Jenson Button, McLaren, 1:08.304
10. Fernando Alonso, McLaren, 1:08.327
11. Sergio Perez, Force India, 1:08.442
12. Esteban Gutierrez, Haas, 1:08.475
13. Pascal Wehrlein, Manor, 1:08.534
14. Romain Grosjean, Haas, 1:08.550
15. Kevin Magnussen, Renault, 1:08.569
16. Daniil Kvyat, Toro Rosso, 1:08.786
17. Jolyon Palmer, Renault, 1:08.939
18. Carlos Sainz, Toro Rosso, 1:09.008
19. Rio Haryanto, Manor, 1:09.116
20. Marcus Ericsson, Sauber, 1:09.137
21. Felipe Nasr, Sauber, 1:09.557
22. Nico Rosberg, Mercedes, 1:10.959