We reached a general agreement with Manchester United on the transfer of Jadon Sancho, pending full completion, as there are still some formalities to agree on and the medical check to be completed.
City will take a 2-1 lead to Dortmund, knowing the German side could seal progress with a 1-0 win on Wednesday on the away goals rule.
"If you think of the consequences or goals you have to score or concede, you forget what you have to do," he told a news conference on Tuesday. "It doesn't matter what happens in the first leg, you have a chance in the second.
They then earned a nervous 3-2 victory at VfB Stuttgart on Saturday to keep alive their slim hopes of qualifying for the Champions League next season.
"Belief is big but belief alone will not be enough," Terzic told a virtual news conference on Tuesday. "We played a good game last week and showed we can keep pace with a top team.
A 1-0 home win, or victory by at least two clear goals, on Wednesday would send Dortmund into the semis to face either holders Bayern Munich or Paris Saint-Germain.
"It's part of the game. In the last 10 minutes they had other chances. They are fast and can do it. When they defend in the way they were doing, you have to stop them running," he said. "We didn't do that.
With Sergio Aguero leaving the Etihad Stadium at the end of the season, City have been linked with Haaland in British media reports and Guardiola will get a closer look at him on the pitch in Tuesday's Champions League quarter-final first leg.
Guardiola last week described the prospect of another record breaking transfer in the close season as "impossible", though on Monday he softened that stance by claiming a 100 million-pound signing was possible.
The players marked the start of their quest to qualify for the tournament by protesting against the Gulf state's alleged treatment of workers before kick off in their opening match.
"FIFA believes in the freedom of speech, and in the power of football as a force for good," the organisation said in a statement.