A smartphone displays the Bitcoin GBP market value on the stock exchange via the Yahoo Finance app.

A difficult week for bitcoin investors may get much worse, according to Renaissance Macro Research.

The firm's head of technical research, Jeff deGraaf, said he would recommend betting against bitcoin if the cryptocurrency broke through its key year-to-date support level.

"Parabolic moves are notoriously dangerous for short‐sellers … Usually a top develops that often appears as a descending triangle over months, with reduced volatility and little [fanfare]," deGraaf said in a note to clients Thursday. "Once the top is complete on the support violation, the security in question can often be considered permanently impaired or even 'game‐over'. We are of course referencing Bitcoin as exhibit 'A' in today's market."

Source: Renaissance Macro Research

DeGraaf is one of the most respected chart technicians on Wall Street over the last two decades. He has been ranked the No. 1 technical analyst by Institutional Investor Magazine for more than 10 years across his career. In 2014, he became a member of Institutional Investor's Research Hall of Fame.

The price of bitcoin is down roughly 14 percent over the past week. The cryptocurrency fell about 6 percent on Wednesday after the U.S. Securities and Exchange Commission delayed a decision on a proposed bitcoin exchange-traded fund. Bitcoin is down about 50 percent so far this year, according to Coinbase data.