Molesley felt the Shrimpers 'struck gold' to recruit a stopper of Bass' ilk at short notice to cover No1 Mark Oxley.
However, the Pompey academy graduate suffered an injury on his debut on Saturday – only hours after arriving at the League Two outfit.
Bass was withdrawn at half-time in Southend s goalless draw with Salford and replaced by rookie Harry Seaden.
Having recently recovered from a fractured leg, the 22-year-old was today due to undergo a scan to discover the extent of his setback.
Should he be forced back onto the treatment table, Southend will aim to recruit a new keeper.
But signing someone the quality of Bass will be difficult.
Molesley told the Southend Echo: ‘We will have to find out how Alex is before anything else but we certainly can’t run with just one goalkeeper in Harry Seaden.
‘We will have to look to rectify that but good goalies are few and far between.
‘We struck gold with Alex but most goalkeepers are No2s and the clubs just won’t let them out.
‘If they’re not number twos then they are very young lads but we already have a very good young goalkeeper of our own in Harry.
‘We will just have to wait and see what tomorrow brings.’