LIVERPOOL, England (Reuters) - Liverpool must hit the ground running in their first Champions League game against AC Milan as a tough group also including Atletico Madrid and Porto will leave no room for error, manager Juergen Klopp said on Tuesday.

Liverpool and Milan contested two finals in 2005 and 2007, with both sides winning one title each, and Klopp said the Group B fixture at Anfield was among the "must-watch" games in the first stage of the competition.