SHANGHAI, China - Aston Martin were concerned the intensity of Formula One's 24 race calendar might lead Fernando Alonso to call it a day instead of signing a contract extension for at least two more years, team principal Mike Krack said on Thursday.

The 42-year-old double world champion, whose new deal was announced last week, has been instrumental to the British-based team's march up the grid after Canadian businessman Lawrence Stroll took control in 2018.