Russia's invasion of Ukraine has left virtually no asset immune from heart-stopping swings.
The cybercurrency trading platform won't pre-emptively ban all Russians from using Coinbase, he said.
The intensifying war in Ukraine is prompting investors to look for safe havens.
In recent weeks he's said that bond traders are overpricing a hawkish Fed, and that recession fears are overdone in small-cap stocks.
Bitcoin dipped below $40,000 level over the weekend and kept weakening as the Ukraine crisis deepened.
Small caps slid into a bear market last month before staging a modest revival.
Technical analyst Rich Ross sees further declines ahead for the S&P 500.
The price of Bitcoin appears positively correlated with proxies for consumer-price risk, firm analysts said.
Citi is bullish on markets outside of the U.S. and prefers defensive sectors such as consumer stables and health care.
Fed tightening, the pandemic and Ukraine tensions have created a tsunami of unknowns for investors.