Roberto is confident Olympiacos will have no hangover from their weekend loss to Atromitos as they visit Malmo in the UEFA Champions League.
The Greek champions started their Group A campaign with a fantastic 3-2 home victory against La Liga holders Atletico Madrid.
Michel's men followed up with a 3-0 win against Veria in the Superleague before defeating Panachaiki 1-0 in the Greek Cup.
However, Olympiacos travel to the Swedbank Stadion on Wednesday on the back of a disappointing 1-0 setback at Atromitos.
Goalkeeper Roberto is sure the loss was just a blip, though, and is confident Olympiacos can make it two wins from two when they meet the Swedish champions.
"[Atromitos] was an important game for us," he told reporters. "We saw it as an important game, we wanted to win.
"We have an obligation to win all games and now we play [another] important game, but [the loss] makes no difference.
"I am very optimistic [we can beat Malmo]. I believe that this is a unique opportunity that we have to start the Champions League with two consecutive wins. We are ready and we will try our best to do so."
Dimitris Siovas made an eagerly awaited comeback from a broken ankle sustained in January when he played in the Greek Cup, but a thigh injury rules him out against Malmo.
David Fuster (groin) and Leandro Salino (thigh) are also doubtful ahead of the match.
For Malmo, the match represents an opportunity to put their first points on the board after a suffering a 2-0 defeat at Juventus in matchday one.
Age Hareide's men are playing a home match in the competition proper for the first time since November 1990 and, having not conceded at home during three qualifying rounds, Malmo will be confident of causing an upset.
Hareide's side are in good form domestically, Emil Forsberg bagged a hat-trick as Malmo came from behind to defeat Mjallby 4-1 at the weekend.
He now has 13 league goals to this name this term - his best return in a season.
Malmo are proving to be solid in defence, too, goalkeeper Robin Olsen has kept 10 league clean sheets this season, more than any other team in the league.
Defender Ricardinho returned from a month-long lay-off with a knee injury to face Mjallby at the weekend and should be in contention, but the match is likely to come too soon for Simon Thern who has recently resumed full training after breaking his fibula in July.