The Blues crashed out of Europe's elite competition at the group stage last season - so becoming the first reigning champions to fail to make the knock-out phase of the competition.
After Jose Mourinho's men suffered a shock 2-1 home loss to Basel in their Group E opener in midweek, Ivanovic has called on the Blues to up their game for their next outing at Steaua Bucharest on 1st October.
Chelsea lost 1-0 at Steaua in the first leg of the Round of 16 stage of the Europa League last year, before a 3-1 second leg home victory saw them progress and they eventually went on to win the trophy.
Ivanovic knows it will be tough to win in Romania, telling the Sunday People: "We can't forget how much effort we put in last season to get into the Champions League.
"We cannot waste it. We have to play hard, we have to train hard every day to improve as a team now.
"Our season is long and we have to react and recover well. Before the next international break we have the Steaua game which is so, so important.
"We all remember how difficult it was there last year when we lost and we know it will be a difficult game, but we have to stand up and fight.
"The atmosphere there is tough, everybody knows how hard and how difficult it is to win there, and Steaua will be motivated for certain.
"But we are a big club and we have big players - we have to show that in every game from now on."