Stroll missed the Eifel Grand Prix at the Nurburgring due to illness, being replaced at the then-called Racing Point team by Nico Hulkenberg.
The Canadian later revealed he had tested positive for COVID-19 but following a negative test he was able to return to the cockpit in Portugal.
Stroll struggled on his return to the cockpit at Portimao, retiring from the race after a collision before finishing 13th in Imola, and has now revealed that the after-effects of contracting the virus were still taking a toll on his physical and mental fitness.
“COVID put me out of the German grand prix and it probably affected me quite a bit for the following two grands prix,” Stroll said at the launch of the Aston Martin AMR21.
“Just no energy, physically, and not in the best place mentally. I think I underestimated how much of a toll the virus would take on me, and I did struggle physically in those races.”
Stroll then regained form in Turkey by taking a stunning maiden pole in the rain, but rues the fact that his mid-season dip, which also included a nasty shunt in Mugello, cost him and his team a lot of championship points.
Racing Point eventually had to cede third place in the constructors’ championship to the more consistent McLaren team.
“After that rough patch I was back on form in Turkey, so I started to get my form back”, he added. “But we lost of a lot of world championship points, there’s definitely a lot of things to learn from that experience.
“On a positive note, we did finish off the season much stronger, but I think the competition was much stronger towards the end of the year.
“Not the same as the beginning of the season where we were often cruising fourth and fifth with both cars, sometimes even better than that.
“The game changed, the competition between the teams, and I think it’s going to be a very competitive midfield once again. We have to get our head down and do the job.”
Along with Stroll, Sergio Perez and Lewis Hamilton were also forced to sit out races in 2020 following a positive COVID-19 test. Lando Norris, Charles Leclerc and Pierre Gasly have since also tested positive during the off-season.