Innovation is the key to Apple's future, top tech analyst says

Apple (AAPL)'s ability to innovate is a major question for investors as they look back on CEO Tim Cook 's five-year tenure, according to one top tech analyst.

"In the last five years, the watch is really the only new incremental product and its success to date has been relatively modest," Toni Sacconaghi, senior research analyst at Sanford C. Bernstein, said Wednesday on CNBC's "Squawk on the Street." "The iPhone has continued to do well, but that was a product that was launched before Tim became CEO."

While Apple's stock price has doubled under Cook's tenure, outpacing the S&P 500 (^GSPC), it has lagged the Nasdaq (^IXIC). The tech-heavy index has outperformed the stock over the same period, rising about 112 percent.

Sacconaghi said, however, that research and development spending at Apple, as a percentage of total spend, remains relatively low compared to its competitors.

"[Cook has] done a good job in recent years in increasing that and so the fruits of that ramped up R&D are probably still not yet felt," he said.

Tim Cook succeeded the terminally ill Steve Jobs at Apple on five years ago this week.