Ireland prop Marcus Horan has emerged as a major injury worry for tomorrow's Triple Crown clash against Scotland.
Horan has a slight calf strain and will be replaced by Simon Best if he is not fit for the Murrayfield encounter.
Ulster's Bryan Young has been called up as cover.
Denis Hickie, meanwhile, resumed light training in Edinburgh today after withdrawing from yesterday's session with a muscle spasm in his back.
A final decision on his fitness will be made tomorrow morning.
Geordan Murphy was called up to the squad last night as precautionary cover.
However, should Hickie fail to regain full fitness, his place in the team will be taken by Ulster's Andrew Trimble, with Murphy starting on the bench.