The move looked set to be completed last week after the Hammers agreed a fee with Middlesbrough for the 32-year-old stopper, but manager David Moyes confirmed the deal was held up as Randolph is now suffering from a thigh injury.
He'll provide competition for Lukasz Fabianski, who is now out injured with a hip injury that occurred after surgery.
Now with a fee agreed upon what remains to be seen is whether the West Ham United hierarchy actually take the risk of bringing on the 32-year-old or wait it out until the end of the season.
West Ham chiefs are fully aware of a potential backlash if they were to sign a player who is instantly forced to spend time on the treatment table.
"I had two great years at the Club previously and still have a lot of friends here, so I had no hesitation in coming back", he added.
The 32-year-old opted to join Middlesbrough in the summer of 2017 after failing to dislodge Adrian as the Hammers' number one, and has gone to play 106 Championship games for Boro - where he was an ever-present in his first two seasons.
"I'd like to thank everyone at Middlesbrough - the management, staff, players and fans - for their support".
"This opportunity was simply too good to turn down".