Romano reported on Wednesday that the Japan international has already passed a medical in London, with a contract expected to be signed within 48 hours, while BBC Sport's Sami Mokbel confirmed Palace are proceeding with the move after a trial spell that convinced manager Pierre Sage of the 27-year-old's fitness.
Crystal Palace had already agreed broad personal terms before the trial began, with the final decision left to Sage given Tomiyasu's history of injury problems since leaving Arsenal. Tomiyasu joined Palace's pre-season camp in Como and featured for around 30 minutes as a substitute in a 3-1 friendly win over Al-Ula, having been an unused substitute against Lens the previous week.
The versatile defender made 84 appearances for Arsenal, largely playing at right-back and centre-back, before his contract was terminated by mutual consent in December 2025, after which he joined Ajax and made eight appearances for the Dutch club.
He also featured for Japan at the World Cup, starting twice in three appearances as they reached the last 16. Sage is expected to deploy Tomiyasu on the left side of a back three, filling the gap left by Maxence Lacroix's £52m move to Chelsea, which prompted Palace to prioritise defensive reinforcements this summer; the club have already added centre-back Oscar Mingueza and are in advanced talks over an £11m deal for Zavier Gozo.
Palace are also weighing up a move for Solly March, who left Brighton at the end of last season. The 32-year-old winger has been recommended internally at Selhurst Park, with the club also holding an interest in a possible loan for Chelsea's Josh Acheampong and in Brest centre-back Raphael Le Guen, according to BBC Sport.
A reunion with Tomiyasu would also reconnect him with international team-mate Daichi Kamada, with the pair having played alongside each other 50 times across their careers, including a spell together at Belgian side Sint-Truiden, while he would also cross paths again with former Arsenal team-mate Eddie Nketiah, having made 53 appearances together at the Emirates.