Alonso, who guided Bayer Leverkusen to a domestic double in 2024 and remained in charge at Real Madrid until January, is expected to end Chelsea's managerial turmoil. Last season, the Blues cycled through three head coaches: Enzo Maresca, fresh from winning the Club World Cup, departed after a boardroom dispute at the start of the year.
He was replaced by Liam Rosenior, whose long-term contract was terminated after less than four months. Englishman Calum McFarlane then stepped in on two interim spells.
The Premier League is familiar with Alonso from his playing days at Liverpool FC, where the former strategist plied his trade from 2004 to 2009.