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."
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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)
