Global markets are riding a "high" on central bank money printing , but a change at the top of the Federal Reserve posed the biggest threat to the rally, Bob Janjuah, Nomura's uber-bearish strategist, told CNBC on Friday.
Janjuah said Janet Yellen, Fed vice-chairman since 2010 and a likely successor to Bernanke when he steps down in January 2014, had the potential to scare the bond markets.
"A client said to me a few weeks ago that if Karl Marx was in charge of the world, he'd have Janet Yellen as his central bank governor. She is far looser or more dovish than Bernanke," Janjuah said on CNBC Europe's "Squawk Box."
"My issue with somebody like Yellen is that she's potentially perceived as such a loose cannon - so loose - that it would scare the bond market , whereas Bernanke has built up a certain level of credibility with the market."
(Read More: Central Banks Gone Wild: What Can Investors Do? )
Yellen is seen as one of the most dovish members of the Fed's policy-setting committee. She has supported the continuation of the Fed's unconventional asset purchase strategy to get the economy growing, while other members have called for an end to the purchases.
Janjuah said "QE infinity" had driven markets to new highs but that rally could end when Bernanke leaves.
(Read More: I'm Not Confident About US Markets: Jim O'Neill )
"The message from me is that anyone who is different is a risk for the market," he said. "When we transition from one Fed chairman to another, things tend to happen. When we went from Volcker to Greenspan in October 1987, markets dropped up to 35 percent...so any change in that figure head and chairman's role is a risk for the market," he added.
"The big one for me isn't so much in the detail of what the Fed might, or might not do in the next few months, it's the fact that Bernanke may well not be in that job come January next year."
-By CNBC's Holly Ellyatt, follow her on Twitter @HollyEllyatt
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