The 34-year-old, who made 55 Premier League appearances in three years with the Reds, has played for Real Zaragoza, Stoke City, Wolves, FC Pune City, Wigan Athletic, Tampines Rovers and Bury since leaving Anfield in 2009.
Pennant was once the most expensive trainee in history when he joined Arsenal from Notts County for £2million in 1999, while he featured in Liverpool's 2007 UEFA Champions League final defeat to AC Milan in 2007.
Ex-Premier League trio Paul Konchesky, Jamie O'Hara and Kevin Foley are also at Ricay, who compaign in the Isthmian League Premier Division.