Conforto and Cano were chasing after a pop fly by Howie Kendrick near the right-field line in the fifth inning when Cano's shoulder connected with Conforto's jaw. Conforto was slow to get up and came out of the game after a long conversation with manager Mickey Callaway and trainer Brian Chicklo.
"He hit the ground hard," Callaway said of Conforto. "He hit his head on Cano's shoulder, he hit the ground. He was kind of dazed. We knew right away we were going to have to get him out of there."
Conforto will not accompany the team to Florida for a three-game series with the Miami Marlins that starts Friday. He will take the train from Washington to New York for further medical evaluation.
Conforto hit a three-run homer to right in the third inning -- his third homer of the week.
Earlier, Mets left fielder Jeff McNeil left in the middle of the third with abdominal tightness. Calloway said he will be evaluated Friday. McNeil has a .354 average, second in the majors, with two home runs and 14 RBIs.
McNeil told reporters he has had four hernia surgeries and sometimes experiences tightness that takes a day or two to go away.
"It's not something I'm worried about," McNeil said.
The Associated Press contributed to this report.