Dekker, a two-time Dutch champion, was set to help Evans in this year's July 4-26 race but found out Wednesday that a sample from December 2007, kept for later re-testing, had tested positive for the banned blood-booster EPO.
On paper it disrupts the plans of Evans, a runner-up the past two years on the world's biggest bike race and one of a handful of real challengers to Spaniard Carlos Sastre's 2008 crown.
However the 32-year-old Australian put a positive spin on the incident, which means Britain's Charly Wegelius comes in to replace the disgraced Dutchman.
"We're here as a team to do what we can, and unfortunately this announcement changes our plans a little bit... but we have time," Evans told NOS.nl.
"Charly Wegelius is on his way here and we'll still concentrate on doing the best Tour we can. This year our team had 11 riders worthy of riding the Tour de France and of course there are only nine places. Now we're down to 10 riders and there are still only nine places [for the Tour squad].
"Fortunately we had a team strong enough where we had that depth in numbers and we could have another good rider who we hope is going to be at his best and do the job that we need."
Evans finished second behind Sastre last year having come second best to this year's big favourite, Alberto Contador of Spain, in 2007.
On both occasions the support from Evans's team, in comparison to those of Contador and Sastre, was arguably inferior although the Australian has never openly criticised his teammates.
This time around, in Belgians Jurgen Van den Broeck and Johan Vansummeren, and fellow Australian Matthew Lloyd, Evans may have found the teammates who can accompany him for as long as possible in the crucial mountains stages.
However off the bike, Silence are still reeling from the news of Dekker's positive test - which dates from when he rode for his former team, Rabobank.
"I'm very disappointed," said Silence team manager Marc Sergeant. "It happened when he was not competing for Silence and was at Rabobank, but still that doesn't make the news any less welcome."
It is not the first time the Dutchman has courted controversy. In August last year it was reported that he was not selected for the Tour de France because of abnormally high blood parameters, an indication, though not proof, that blood manipulation has taken place.
Dekker has also collaborated in the past with Italian trainer Michele Ferrari, who has been controversially linked with administering EPO since the 1990s.
Ferrari is best known for having worked with seven-time Tour de France champion Lance Armstrong, who in 2001 admitted he had collaborated with the Italian doctor.
The use of EPO boosts the oxygen-rich cells in the blood, thus allowing athletes to work harder and for longer.
© AFP 2009