Britain's Paul di Resta will make a shock return to Formula One at the Hungarian Grand Prix after Felipe Massa was ruled out through sickness.
Massa, 36, had been given the all-clear by the FIA to continue his participation on Saturday morning after he was taken to hospital following complaints of dizziness. But the Brazilian had to cut short his run in final practice and completed just 12 laps after falling unwell again.
Williams reserve driver Di Resta, who last raced in the sport back in 2013, had not tested this year's car and was thrown into the deep end in qualifying later on Saturday.
"After feeling unwell during practice in Budapest on Friday and Saturday, Felipe Massa will not drive for the remainder of the Hungarian Grand Prix weekend," Williams said in a statement released ahead of qualifying.
"Felipe visited the medical centre and the MH EK Honvedkorhaz hospital for precautionary tests on Friday, after feeling unwell and dizzy during FP2. He was cleared to take part in Saturday's practice session by the FIA medical delegate, but he felt unwell again during FP3 and has made the decision to withdraw from the weekend.
"Williams supports Felipe's decision and the team will work with him to ensure he makes a full recovery, with a view to return to the race track for the Belgian Grand Prix.
"Following this decision, the team's Reserve Driver Paul di Resta will drive alongside Lance Stroll for the remainder of the Hungarian Grand Prix weekend."
Di Resta has 58 grand prix starts under his belt after racing at Force India for three consecutive seasons in between 2011 and 2013.
His participation will be his first since the season-ending Brazilian Grand Prix nearly four years ago, and his only taste of this year's Williams will have been in the team's simulator at their Oxfordshire base.
Di Resta, 31, had also been due to deputise for pundit Martin Brundle in the Sky Sports commentary box in Hungary. Brundle is absent from this race after he was taken ill moments before the British Grand Prix a fortnight ago.
Speaking ahead of the announcement, Di Resta said: "I'm ready to pounce if Felipe needs a stand in. You're very anxious. Nervous but very excited. It's a tricky little track and You have to be very committed and confident.
"You just have to get in the car and do the best-possible job. There's no pressure out there. I hope I would do as good a job or better than anyone else."
Claire Williams, the team's deputy team principal, added: "It is unfortunate that Paul did not even get this morning's hour which would have been useful, but he is an experienced driver.
"He has not competed in a race weekend for a few years, but having someone like Paul you are going to have the confidence that they will deliver."
Di Resta will be the third British driver on the grid this weekend alongside Lewis Hamilton and Jolyon Palmer.