The referee initially produced a yellow card but following a check with the Video Assistant Referee (VAR) he changed his decision and showed the former England international a straight red card.
"I have no arguments," Rooney, who is England's all-time leading scorer, told reporters. "It wasn't malicious, I didn't try to hurt him.
"But obviously I caught him. I was expecting (a red card) really when the referee gave me the yellow. It's the right call."
It was Rooney's first red card since 2014 and the seventh of his career for club and country. DC United, who were losing 3-0 at the time, lost 4-0 as Rossi completed a hat-trick.
(Reporting by Rohith Nair in Bengaluru; Editing by Toby Davis)
