Former British & Irish Lions lock Kruis made a long-planned move to Japan to play for Saitama Wild Knights in 2020, when Saracens were relegated for salary cap breaches, which put his international career on hold.
He had won 45 caps for England and another for the Lions on the drawn 2017 tour of New Zealand. Kruis was an England regular who became known for his lineout prowess.
Kruis launched fourfive, a Cannabidiol (CBD) business, with former Saracens and Wales lock Dom Day, in 2018.
Kruis had expressed his desire to return to Saracens next season, but has now decided to pursue the business when the Japanese season ends in May.
The business is proving demanding time-wise, with the product stocked in Boots and other major retail stores, and partnerships with Saracens and Leicester Tigers.
“I’ve been very lucky to still have some really good offers on the table, whether it’s in Japan or some clubs back home, but I need to cut my career short as there’s such an opportunity off-field,” Kruis told The Times.
“Dom has had to go full-time, and we’ve got seven employees. It’s now dragging me out of rugby, and needs my 100 per cent attention.
“It’s a huge decision not to try for all those things, but this is something in front of me I can’t ignore.”