Some of cycling’s biggest names are scheduled to line up Sunday for the opening stage of the five-day Mallorca Challenge, but a breakout of the flu is keeping some top stars away from the annual Spanish season opener.

A nasty bout of flu is taking its toll on the European peloton, with such riders as Oscar Pereiro and two-time champ Alejandro Valverde (both Illes Balears) and Gilbert Simoni (Saunier Duval-Prodir) all doubtful for Sunday’s 100km opener along Palma de Mallorca´s historic bay.

"Several of our riders have been very sick with the flu and they’ve been sent home," Illes Balears sport director Eusebio Unzue told VeloNews. "It’s better to have these problems now than later."

Scores of other big names will be ready to step into their void. Most teams are working in as many as dozen riders into their lineups in the unique format that let’s riders start and pull out of "stages" as they see fit. There’s also an unofficial overall cumulative time for GC taken for riders who participate in all five legs.

Teams are also using the usually sunny Mediterranean Island of Mallorca as a staging ground for one final, pre-season training camp to hone form ahead of the season’s first important races.

VeloNews spied Rabobank, Illes Balears and Milram on group rides while scouting out this week’s route today.

Ten ProTour teams are among the 21 teams taking part in the 16th annual Mallorca Challenge that marks the debut of the Spanish racing calendar.

Among the teams here are Astana, Illes Balears, Rabobank, Quick Step, T-Mobile, Milram, Liquigas, Discovery Channel, Saunier Duval, Euskaltel-Euskadi and Gerolsteiner. The rest of the field is rounded out by Spanish continental teams.

Among the other big names include Peter Van Petegem and Tom Boonen (Quick Step), Oscar Freire (Rabobank), Erik Zabel (Milram), Magnus Backstedt and Filippo Pozzato (Liquigas), Iban Mayo (Saunier Duval) and Stefan Schumacher (Gerolsteiner).

Members of Spain’s track team will also be racing on Sunday as a warm-up for the world track championships set to be held in Palma de Mallorca in March.

The race will open Sunday in homage to fallen local rider Isaac Gálvez, who died this winter in a horrific crash on the track. Gálvez’s two brothers will be on hand for a special ceremony for the Mallorcan reside.