Apple shares have performed miserably in the past week, falling nearly 5 percent even as stocks as a whole are essentially flat. And if Apple continues to lose ground, key indices could be in trouble.
Apple makes up about 4 percent of both the S&P 500 and Dow Jones industrial average, and some 13 percent of the Nasdaq 100. That means that investors who hold the popular (SPY), (DIA) or (QQQ) ETF may incidentally have oversize positions in the tech giant.
Due to its heavy weighting, Apple's weakness "is a problem right now for the market, and there's really no way to get around it," Larry McDonald of Societe Generale said Thursday on CNBC's "Trading Nation."
Oppenheimer head of technical analysis Ari Wald agrees that Apple "can continue to pressure the market as a whole," particularly as shares look to stay weak for some time.