The S&P 500 is testing its 50-day moving average and lower channel boundary, with momentum indicators flashing warning signs. A move below the 6630 pivot would confirm a deeper pullback, after the index failed to retest its October high, Société Générale's FX analysts note.

Negative momentum signals risk for S&P 500

"S&P 500 is probing the 50-DMA and the lower limit of the channel within which the up move since August has evolved. Daily MACD has been posting negative divergence highlighting receding upward momentum. However, a break in price structure will be crucial for confirming a short-term pullback."

"A brief pause cannot be ruled out. The index has so far formed a lower high near 6870pts than the one achieved in October at 6920pts. Break below recent pivot low of 6630pts could denote possibility of a deeper down move."