The 23-year-old spent the second half of last season with the League One club, only to suffer a hamstring injury that ended his campaign prematurely.
Nlundulu scored once in four appearances for the Robins, who finished 15th in the third tier – the highest league finish in the club’s history.
The England youth international has made 16 appearances for Saints at first-team level, scoring his only goal on his only start, against Shrewsbury in the FA Cup in January 2021.
