The pair were lavished with praise when Juve got off to a flying start, but their recent below-par performances have contributed to their team picking up just two points from their last three Serie A games.
Former Werder Bremen playmaker Diego earned comparisons with Michel Platini for his performances in earlier wins over Chievo Verona and AS Roma, but has not been so sharp after returning from a hamstring injury.
Melo, who has also had trouble with his thigh, has been sloppy at times in the holding position and his play led to the opening goal in a 2-0 defeat at Palermo last time out.
"Melo has not suddenly become a no-hoper, he's just had a few problems," defender Fabio Cannavaro told reporters. "We know what he's worth."
Melo will be hoping the rest during the international break will help him regain his sparkle against former club Fiorentina, who along with Juventus have 14 points from seven games.
Cannavaro may return for Juve from a thigh problem having played in Italy's 3-2 win over Cyprus on Wednesday after being cleared of a doping charge earlier this week.
If he does, he will have to keep an especially close watch on Alberto Gilardino.
The in-form forward hit the late hat-trick that gave the Azzurri victory on Wednesday having scored the last-gasp equaliser that earned them a 2-2 draw in Ireland on Saturday to ensure World Cup qualification.
Juve's Mali midfielder Mohamed Sissoko is tipped to play for the first time since breaking a bone in his foot in March.
Captain Alessandro Del Piero is back in training after a hamstring problem but is not expected back for two weeks and midfielder Claudio Marchisio is out for a month after knee surgery.
Champions and joint leaders Inter Milan, who are two points ahead of Fiorentina and Juventus, take on fifth-placed Genoa away later on Saturday.
Genoa's city rivals Sampdoria, who share the top spot with Inter, meet Lazio in Rome on Sunday.
AS Roma, who visit struggling AC Milan in Sunday's late game, will be seeking to continue their good run of results since Claudio Ranieri took over, although captain Francesco Totti is a doubt after taking a knock to his knee.
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