Caines on trial with Oxford
The 26-year-old centre half played the first half during United's opening pre-season friendly defeat to Oxford City last night.
The Birmingham-born defender has struggled with injuries in the past two seasons and was a bit-part performer for the Robins last term.
Signed after his release from Walsall in 2004, Caines made 171 appearances in five seasons with the Robins, scoring eight goals.
Meanwhile former Robins forward Damian Spencer scored on his first appearance for new club Kettering Town.
Spencer scored the only goal as the Poppies, who also included former Forest Green midfielder Lee Fowler, beat Hinckley United 1-0.
Three other former Robins stars are currently plying their trade for League One club Wycombe Wanderers.
Chris Westood and Lewis Montrose, both of whom had successful loan spells with the Robins last season, have both agreed permanent deals with the chairboys.
Former Leeds United midfielder Ian Westlake, who made 26 appearances for the Robins last term, is currently playing for Wycombe on trial.
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