A stock analyst has downgraded his rating on Micron stock based on concern that Micron likely will buy a struggling German memory-chip manufacturer.

UBS AG analyst Uche Orji says Micron’s purchase of Qimonda AG is “highly probable,” according to an online report Tuesday in Tech Trader Daily.

He says the deal would be good for Micron in the long run but would dilute the value of Micron’s already-battered stock.

His report and another analyst’s downgrading of Micron stock helped send Micron stock to a 15-year low Tuesday morning. It traded as low as $3.61.

Micron’s previous 52-week low was $4.12.

A Micron executive suggested in a Boise radio interview in late August that Micron might buy Qimonda.

Buying Qimonda could delay Micron's plans for a new manufacturing unit in Boise.