Belfast-born Rice started his career in the Arsenal academy and went on to lead the side in the 1979 FA Cup final win over Manchester United, before the Northern Ireland defender moved into coaching after finishing his playing career at Watford.
The 64-year-old stood down from his role as assistant manager to Arsene Wenger at the end of last season, a position he had held since the Frenchman arrived in 1996.
A club statement read: "We can sadly confirm Pat Rice is in hospital receiving treatment for cancer.
"Everyone at Arsenal Football Club sends him our best wishes. Our thoughts are with Pat and his family."
Source: PA
Source: PA