Lewis Hamilton's preparations for Belgian GP qualifying have been compromised after he crashed out of Practice Three - in a session Ferrari underlined their status as favourites for pole position.
Hamilton hit the barriers at the fast Fagnes corner and damaged the front-left of his Mercedes after losing control as he ran over the kerb.
Mercedes are now working to repair Hamilton's car in time for qualifying, which begins at 2pm live on Sky Sports F1.
"We will be replacing both front corners (suspension and wheel assemblies), nose, barge boards and floor," confirmed a Mercedes spokesperson. "Barring unexpected nasty surprises, we believe we can complete all of the work in time for the start of qualifying."
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Already complicating the world champions' weekend is the supreme pace of rivals Ferrari, with the Scuderia finishing first and second for the third consecutive practice session.
Charles Leclerc outpaced Sebastian Vettel again with his best lap of 1:44.206 nearly half a second quicker than his team-mate, who locked up at La Source on his first lap following the Hamilton-triggered red flag.
"It is an open goal for Ferrari. It does look like they're very strong," said Sky F1's Damon Hil..
Valtteri Bottas was close behind Vettel in third place for Mercedes, with Renault's Daniel Ricciardo unexpectedly ahead of Max Verstappen in fourth.
Racing Point's Sergio Perez was forced to revert to Mercedes' older-spec engine after a problem in second practice, but the Mexican still maintained a top-six position in P3 and appears in the hunt for a strong qualifying session.
Running customer Ferrari engines, Alfa Romeo's Kimi Raikkonen and Antonio Giovinazzi ran strongly in the disrupted session to both finish in the top nine, with Pierre Gasly a promising 10th on his Toro Rosso return.
Gasly's replacement at Red Bull, Alex Albon, finished at the foot of the order but the 23-year-old was clearly concentrating on race pace with the arrival of Honda's latest engine locking him into a back-of-the-grid start on Sunday.