28-year-old Grubb, a product of his hometown club Weston-super-Mare's youth system, made over three-hundred appearances for the Seagulls before joining Forest Green for an undisclosed fee in January 2018.
Grubb, who can also operate as an attacking midfielder, has found match minutes hard to come by so far this season, making just three starts in League Two with his only goal coming in the 3-2 home win over Southampton Under-21s in the EFL Trophy.
The Saddlers are said to be joined by Newport County in the race to land Grubb, however, neither team has confirmed their interest with both preferring to play their cards close to their chest.