Inter Milan playmaker Wesley Sneijder failed to train on Friday after being sent home with a fever, the Serie A leaders said on their website, making the in-form Dutchman doubtful for Sunday's derby with AC Milan.
Coach Jose Mourinho was already sweating on the fitness of midfielders Dejan Stankovic, Sulley Muntari and Thiago Motta with the latter the only one to train fully with the group.
If the four are unavailable, Mourinho will have to take a risk and play a three-man attack on Sunday.
Milan, second in the table and six points behind Inter with a game in hand, have as many injury worries as Inter with top defender Alessandro Nesta almost certainly out with a leg muscle problem.
Giuseppe Favalli and Kakha Kaladze are battling to replace the centre back.
Alexandre Pato and Gianluca Zambrotta have already been ruled out while Clarence Seedorf may have to be content with a place on the bench after recovering from a knock.
Inter president Massimo Moratti is slightly nervous ahead of the sell-out game, which could have a big bearing on the title race.
"I fear the unpredictability of Ronaldinho but I trust in the character of my team," he told Rai television.
Antonio Candreva could make his Juventus debut at home to AS Roma on Saturday in Serie A's other standout match of the weekend.
The Italy international, signed on loan from Udinese having spent the last year and a half at Livorno, has a good chance of starting given injury and suspension have hit Juve's midfield.
"I didn't expect to be here so soon. I have only seen many of my team mats on TV," the Roma fan, who will still celebrate if he scores, told reporters.
Roma, who have risen above Juve into third after the dreadful recent form of Ciro Ferrara's side, could pair fit-again Francesco Totti with new signing Luca Toni.
Former Juve coach Claudio Ranieri returns to Turin as Roma boss for the first time since his sacking in May but he could be spared abuse from Juve's ultra fans given their section of the ground has been closed because of racist chanting.
In-form Fiorentina striker Adrian Mutu has given the club a lift ahead of Sunday's game at fellow European hopefuls Palermo by telling reporters he will not leave Florence despite constant media speculation about his future.
Fourth-placed Napoli are without suspended striker Fabio Quagliarella and the injured Ezequiel Lavezzi for Sunday's trip to Livorno, who could start forward Claudio Bellucci after his arrival from Sampdoria.
