Arjen Robben and Franck Ribery could be separated again just a week after they had promised a return to the good times for Bayern Munich.
The pair made a telling contribution in Bayern's 4-0 victory over Hoffenheim last weekend and they stole all of the weekend's headlines as the reigning German champions' title challenge got back on the rails.
However, just three days before this weekend's trip to Mainz, Robben broke down in training, raising doubts about whether he and Ribery will be able to run out onto the field together again this Saturday.
"For Bayern, it is absolutely essential that these two players are on board,'' said Bayern's director of sport Christian Nerlinger in an interview with his club's website, which was recorded just before Robben walked forlornly away from the training field.
"I hope that we remain free of any more injury misfortune.''
According to the Bayern website, Robben had a light adductor injury and ended training early as a precaution, but given the Dutchman's injury history, doubts will remain about his inclusion on Saturday until the team sheet is filled in.
Ribery has declared what his side need to do over the next four weeks, in which eight games in three competitions could make or break their season.
"We have got to put a run together and win all of our games,'' said the Frenchman.
Mainz did, however, get the better of Bayern at the Allianz Arena earlier this season and, after also beating Bayern at their own Bruchwegstadion last year, they will not be a pushover.
However, a win for the Bavarians would take them into their highest league position of the season, at least until Bayer Leverkusen host Stuttgart on Sunday.
Both sides are still trying to keep up the chase on leaders Borussia Dortmund, who have drawn their last two games and will be looking to get back to winning ways against St Pauli, who are fresh from their midweek win over Hamburg, on Saturday.
Hamburg have fallen four points behind the top five as a result of their derby loss and the heat is on coach Armin Veh ahead of another intriguing derby against Werder Bremen on Saturday.
Bremen coach Thomas Schaaf is also under pressure with his side lying just one point above the bottom three and desperately in need of a win to kick-start their season.
Defeat, on the other hand, would see them drop into danger if both Wolfsburg and Kaiserslautern win their away matches at high-flying Hannover and Freiburg respectively.
Elsewhere, in-form Nurnberg host wobbling Eintracht Frankfurt tomorrow night and Hoffenheim face Cologne. Finally, Lucien Favre leads Borussia Monchengladbach for the first time in their home game against Schalke on Sunday evening.