Inter Milan's rise in the Serie A standings has exceeded Leonardo's expectations since he replaced Rafa Benitez as coach at Christmas.
When the Brazilian was appointed to the job, Inter was 13 points behind city rival AC Milan in the Serie A. The club also had finished second to Tottenham in the group stage of the Champions League.
On Saturday, Inter could move into first place if it beats Milan. And on Tuesday, the team meets Schalke in the Champions League quarterfinals after beating Bayern Munich in the round of 16.
''At the time it seemed difficult; to get here and in the way we have,'' Leonardo said Friday. ''To be second in the league and then have the quarterfinal of the Champions League a few days afterward, a lot of things came together.
''A derby is always decided by small details. First off we had to get to second in the table and now it has become a massively important game.''
This time last season Leonardo was in the opposite dugout, where he endured 4-0 and 2-0 losses to Inter in his one season in charge of Milan.
He spent six years at Milan as a player before becoming one of the club's technical directors.
''I think it has been exaggerated about me coming back here as coach of the other team,'' Leonardo said. ''There's a lot of players with connections to both teams and everyone knows about my relationship with the other club. I respect the club and the way they play football.
''I think they are two teams that want to attack and play good football. Both teams have a certain style and of course it is a derby and both teams will want to win it.''
Milan is without former Inter striker Zlatan Ibrahimovic, who is serving a one-match ban for punching Bari defender Marco Rossi.
''He (Ibrahimovic) is a great player and anyone would miss him,'' Leonardo said. ''He is very important for Milan, but whichever strikers Milan puts on the pitch, they will be able to play at the level asked of by Milan.''
Milan coach Massimo Allegri will have three fit strikers - Italy international Antonio Cassano and Brazil teammates Alexandre Pato and Robinho.
Milan is on a three-match winless streak, having followed its elimination from the Champions League by Tottenham with a draw against Bari and a loss in Palermo.
''We have taken one point from two games, but the great thing about football is that everything can change,'' Allegri said. ''We have been in the lead for 21 matches and knew well that we can't win the championship a month out.
''Tomorrow we just need to concentrate on getting a result. It is a massively important match, but more so for Inter than us.''
Along with Ibrahimovic, Milan is without midfielders Andrea Pirlo and Massimo Ambrosini, and defender Daniele Bonera, but Allegri hopes the possibility of opening a five-point lead will inspire his team to snap its winless run.
''Milan will be top until the final whistle,'' Allegri said. ''If we win we will lead by five points with seven games remaining. That wouldn't be bad, but it is true that we have only taken one point in two games.''
