Surprise Spanish league leaders Atletico Madrid stunned Barcelona FC in the quarter-finals, sealing a 2-1 aggregate win this week with a 1-0 home victory, but are still considered the dark horses to win the trophy for the first time.
Antic, who became the fans' hero when he won the Spanish league and cup double with Atletico Madrid in 1996, believes the current side put together by Diego Simeone can be even better.
"Atletico Madrid are the fittest team in Europe at the moment and their confidence will be very high after beating mighty Barcelona," the 65-year-old Serb told Belgrade daily Informer.
"They did it despite their two best players Diego Costa and Arda Turan missing the return leg and hence their surge in Spain and Europe should no longer be viewed as a surprise.
"The club will head into the Champions League semis knowing the other teams will not fancy the prospect of playing them."
Atletico Madrid are top of La Liga with 79 points from 32 games, one more than Barcelona who they visit on the last day of the season and two ahead of Real Madrid, with six games remaining.