Apple is up 18 percent for the quarter, but CM Research rates the stock a sell, and said the tech giant will see its shares plunge by 20 percent this year.

"We've had a buy for about five years, but right now we think there's a gap between the next big blockbuster product and maturing iPhone sales. That means that there's more downside than upside at the moment," CM Research CEO Cyrus Mewawalla told CNBC's "Worldwide Exchange" on Wednesday.

Thematically, Apple is in good shape given its pipeline of projects, according to Mewawalla. He said the company's potential projects like driverless cars and products using artificial intelligence set it up for success in the long term.

The key issue over the next year for Apple is iPhone sales, Mewawalla said. "IPhone sales are set to slow down more than analysts think, especially in China." He sees the Chinese government protecting its own phone market, even more than in the past.

The other unknown: Apple's tax problem, he said.

The European Commission's $14.5 billion tax fine isn't the only penalty Apple and the whole tech sector will have to deal with, according to Mewawalla. "Japan is now considering taxing Apple quite a bit for profits made in Ireland, and a lot of other countries will do that, too."

"That's going to have a kind of 'kickoff' effect in the whole of tech," he added.

Mewawalla does believe Apple could appeal the fine, but it wouldn't get off scot-free. He sees effective tax rates on tech companies going from 4 percent on overseas earnings to 10 percent in three to four years.