But he warned his team must cut out the individual errors that continue to undermine their defensive performances.
Donnarumma was at fault for one of Leipzig's goals, with the Italian unable to prevent a cross from beating him at his near post. However, Maresca was keen to point out that the goalkeeper had produced an outstanding save from Christoph Baumgartner shortly before the incident.
The City manager insisted he had no concerns about his first-choice goalkeeper, while acknowledging that Donnarumma knew he should have done better.
"Not a concern but it's a mistake. We recognise that it's a mistake," Maresca said.
"At the moment I'm not thinking about the goalkeeping situation. A few minutes before the goal he’s done a save that no keeper in the world makes. Gigio knows he was not good with the first goal. He’s going to do better."
Maresca's greater frustration was with City's defensive performance as a whole. Despite scoring three times to secure the victory in Germany, his side conceded twice and gave Leipzig opportunities to get back into the game.
"Both goals are quite silly goals we can avoid," he said. "We are creating many chances in each game but we need to avoid silly goals.
"It's about working more. Understand and analyse. I'm new here, I need to know the players and they need to know me. We can only improve."
The Italian also rejected suggestions that City's defensive problems were primarily down to the team's tactical structure or a lack of balance between midfield and attack.
Instead, he believes individual mistakes have been the recurring issue, with City conceding in each of their previous five or six matches across competitions.
"I don't think in this moment it's a matter of balance," Maresca added.
"In the last five or six games we concede in all competitions [and] they are individual mistakes so it's not about the system or a midfielder to the offensive line.
"It's more individual mistakes that we need to do better to avoid."
Manchester City's victory provided three valuable points in the Champions League, but Maresca knows his side must become more reliable defensively if they are to build on their attacking threat.