The Leipzig goal was disallowed, with Kroos also saying it was a mistake

Leipzig lost 1-0 at home to Real Madrid in the Champions League last 16 first leg last night. Controversy arose over the German club not conceding a goal in this match. After the final whistle, Leipzig coach Marco Rose claimed the wrong decision had been made.
Real won with a great goal by Brahim Diaz in the 48th minute. However, in the second minute of the match, Leipzig's striker Benjamin Sesco sent the ball into Real's net. But the lineman flagged offside on that goal.

Video replays showed Sesco was clearly on the sidelines. But the Video Assistant Referee (VAR) did not change the decision. Another Leipzig player Benjamin Heinrich was offside. Although he did not touch the ball, he blocked the vision of Real goalkeeper Andre Lunin.

Leipzig coach Marco Rose called the disallowance a mistake after the match, saying, "There was a goal that should have been allowed." If we had pursued one goal, things could have been different.
Not only the Leipzig coach, but Real midfielder Toni Kroos also felt the goal should have been disallowed.

"Offside," said Kroos, "because the goalkeeper's vision was obstructed." But the goalkeeper didn't get the ball, so the goal was scored. Real coach Carlo Ancelotti, however, pushed the ball to the referee's court. "You should ask the referee," Ancelotti said of Leipzig's disallowed offside goal. He (the referee) said the (Real) goalkeeper had a problem because of the Leipzig player.'