Barca will face their former striker Ibrahimovic, who left Nou Camp on bad terms at the end of the 2009-10 season, as they visit the Serie A champions for their Champions League quarter-final first leg on Wednesday, the outstanding tie of the round.
"We have to deactivate Ibra and Milan by monopolising possession of the ball," said Guardiola. “He is a very strong player especially in the air. He is unstoppable if he participates a lot in the match.
"We owe him part of a league title. His first six months (at Barcelona) were very good."
Having left Barcelona after only one season in which he helped them win La Liga, Ibrahimovic launched a stinging attack on Guardiola, saying he could not understand why their relationship had broken down.
"I still haven't got an answer as to what the problem was," he said shortly afterwards. "It can't have been the quality (of my football) because there was never a discussion about the football part."
The volatile Swede has enjoyed an excellent season with Milan, scoring 22 goals in Serie A and five in the Champions League.
Guardiola refused to accept that his side, who won 3-2 at San Siro in a group stage match in which Ibrahimovic was among the scorers, were favourites to knock out the injury-hit Serie A leaders.
"The only certainty is that if you don't play too good games, you don't go to the semi-finals," he said. "I expect the best possible Milan team in one of the world's great stadiums."
"I try to transmit to the players the message that they must not let up after winning so much. I wouldn't want us to betray ourselves, knowing that we could be knocked out as a result."