It will take "three months" before Kevin Magnussen is match-fit for Formula 1.
After losing his Haas seat, the Dane spent a full year in sports cars before being recalled by the small American team to replace Nikita Mazepin.
He struggled physically in Bahrain, but team boss Gunther Steiner is happy about the 29-year-old's return to Formula 1.
"I think he's matured over the last year and realised how good it was to be in Formula 1," Steiner said.
"When you are out of F1 you just realise what you lost and making it back in is like a dream."
But Magnussen's real physical struggles only struck in Saudi Arabia, when he said his neck "broke" in Q3 - meaning he could no longer hold his head up in corners.
"It's not that he's unfit," his physio Thomas Jorgensen is quoted by as-web.jp.
"The problem is that he didn't use the muscles he needed in F1. Sports cars don't require as much physical strength as F1.
"It will take some time for Kevin to fully recover. Usually it should take two months during the winter when you can train every day, but now that the season has begun and there are more travel days and races, it's even harder to do your usual routines.
"So it will be another three months before Kevin is in good shape," Jorgensen added.
