"His injury is in the muscle just above the tendon where it joins the knee so it's not an area that gets great circulation. Therefore, it doesn't heal quickly."
Newcastle had earlier sent Carroll to Dubai in the hope that a warm weather break would speed up his recovery ahead of the derby against Sunderland on Sunday, 16 January. Carroll's last game for the Magpies was at Tottenham on 28 December.
There are also concerns about midfielder Dan Gosling, who has suffered a reaction to his return from a long-term knee injury. Gosling made a comeback as a substitute at Sunderland but may now require exploratory surgery.
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