The 31-year has signed an initial one-year contract with the Robins.
"Lloyd has a good track record and has scored goals at this level," said Downing.
"He's got great experience, strength and presence and can lead the forward line.
"He's different to what we have already in terms of his height and strength and will give us that extra firepower.
"Lloyd has been around the scene for a while so we know what he can do and what impressed me was that he was keen to come here.
"We've had a few setbacks with players we've tried to sign over the last few weeks but Lloyd wanted to come to Cheltenham and continue his career with us."