Former Reading FC forward Williams suffered a serious knee injury 32 seconds after coming on in a 3-0 win over AFC Hinksey on December 1. He is due to see a specialist and Robins fear losing him for the remainder of the Hellenic Division One East campaign.
But the club say they will not be pushed into a panic signing and are confident Cooper-Clark can carry the extra burden.
Robins joint player-manager Danny Oliphant declared: "Shane has all the ability in the world. He is getting into great positions and he is starting to use that ability.
"We're definitely getting the best out of him, he's improving every game. It's not only his goals that are important, his hold-up play is excellent and he's learning all the time.
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