With 5:15 remaining in the second quarter and the score tied at 27, the Liberty got out on the break after forward Joyner Holmes grabbed a rebound and passed to Ionescu, who dribbled near midcourt and attempted to ward off the defense of Dream guard Betnijah Laney.
Ionescu then appeared to roll her left ankle and fell to the ground.
The No. 1 overall pick in the 2020 WNBA draft had scored 10 points in 12 minutes prior to her exit. She was replaced in the lineup by guard Jazmine Jones.
Ionescu was coming off a 33-point, seven-rebound, seven-assist performance against the Dallas Wings in just her second professional game.
The Libs started the year 0-2 but looked dominant against the Dream after falling behind 11-0 and then 16-3 in the first quarter.
However, Kylee Shook and Ionescu led the Liberty on the comeback charge, scoring a combined 15 points in a 24-9 run.
Megan Walker entered the lineup in place of Ionescu to start the third quarter. The ex-UConn star was the ninth overall pick in the 2020 WNBA draft.
New York is scheduled to face the Phoenix Mercury next on Sunday at 1 p.m. ET before taking on the Minnesota Lynx on Wednesday and the defending WNBA champion Washington Mystics on Friday. The Liberty have five games between Sunday and August 13.
The WNBA schedule is shorter and more condensed this season with the league forced to alter plans because of the COVID-19 pandemic, so Ionescu could be missing a larger chunk of the season that she would have in a normal year. The team hopes she returns to the court shortly as the young Libs, with seven rookies, continue their development and build chemistry with an eye toward the future.
Ionescu, the first NCAA player to register career marks of at least 2,000 points, 1,000 assists and 1,000 rebounds, won the Naismith and Associated Press Player of the Year awards with the University of Oregon in 2020.