Nico Hulkenberg is to stand in for Racing Point's Sergio Perez at the British Grand Prix, after the Mexican contracted coronavirus.
Perez tested positive on Thursday and revealed he flew back to Mexico after the previous race in Hungary to visit his mother, who had been in hospital.
He will miss at least the two races at Silverstone this weekend and next.
However, German Hulkenberg has not yet been confirmed for next weekend's 70th Anniversary Grand Prix.
Perez said: "I'm extremely sad, definitely one of the saddest days in my career. I knew I had a great car underneath me, and the team has done a fantastic job.
"But it just shows how vulnerable we all are to this virus. I follow all the instructions from FIA and my team.
"After Hungary, I took a private plane to go to Mexico to see my mum for two days because she had a big accident, so as soon as she left hospital I was able to see her.
"And then I came back to Europe, the same way with all the protocols in place. I just got it, I don't know from where.
"Tough moments for me but I am sure I will come back stronger."
Hulkenberg, who was out of F1 after being dropped by Renault at the end of last season, returns to the team he raced for in 2012 and between 2014 and 2016.
Racing Point chose Hulkenberg over Mexican Esteban Gutierrez, who is the Mercedes reserve driver for this weekend and they had a contractual right to call on had they wanted to because of their links with the world champions.
A Racing Point statement said: "Nico's experience of racing in contemporary Formula 1 and his strong track record ensure he is the ideal driver to stand in for Sergio Perez.
"In a bid to minimise disruption and ensure the best possible chance of building upon the team's strong start to the 2020 campaign, Nico's familiarity with the team will prove invaluable."
Racing Point team principal Otmar Szafnauer said: "In Nico we've got a fantastic super-sub who the team knows very well.
"He's certainly being thrown in at the deep end, but he's a fast learner and I'm sure he will get up to speed quickly."
Hulkenberg said: "I was on my way to the Nurburgring for another racing project when the call from Otmar came.
"That was less than 24 hours ago, so it feels a bit surreal for me right now - but I like a good challenge and this is certainly one.
"It's obviously a difficult situation for Racing Point and Checo. He's a buddy of mine, an old team-mate and I wish him a speedy recovery.
"Hindsight's a wonderful thing. We need to look back forensically and work out how he contracted the virus.
"Perhaps we should look at it and change the code and say within the season you should stay within your bubble. But the code is a living document. I don't think he did anything wrong going back to his family. It's no different to Ferrari going back to Italy. He took all the precautions."
Szafnauer said there was still some uncertainty over who will drive alongside Lance Stroll at the 70th Anniversary GP next weekend.
He said there was a question mark over whether Perez had to isolate for seven or 10 days, depending on which UK government guidance applied, as it had changed this week. And there was the question of whether Perez will test negative before next weekend's race.
If Perez is either still in isolation or still positive, Hulkenberg would continue, Szafnauer said.
- Anthony: The unprovoked racist attack that ended a life
- Rise of the Murdoch Dynasty: How did the media empire shape Brexit and Donald Trump?