The Amstel Gold Race winner crashed during the race and suffered a tear to a kidney but the diagnosis came only after the podium celebrations.
Gilbert downed the traditional beer to celebrate his victory but was still feeling pain on his right side and was taken to hospital for examination where the tear was diagnosed.
Recommended was a full week of recovery which ruled out taking his hot hand to Flèche Wallonne and Liège–Bastogne–Liège and perhaps some relief for his rivals.
“When I crashed, I felt pain, but once I remounted and continued the race things became better and better and the pain disappeared," Gilbert said.
"Unfortunately, after the finish, the lower back pain returned, so together with the team doctor, I decided to go to the hospital for a check-up.
"Fortunately, it’s nothing serious, and if everything goes well, in a week I will start training again."
Gilbert will remain under observation at the hospital until cleared to return home.
Despite the setback, Gilbert was satisfied with his Spring campaign, which also netted him a career first victory at the Tour of Flanders.
“It’s one of my best years and looking behind on what I achieved makes me very happy," he said.
"To be competitive in both the cobbled and the Ardennes Classics and to help the team be the best in the world brings me a lot of satisfaction.
"It’s sad I won’t be there for the remaining races of this week because I was in great condition, but our squad is a strong one and I’m confident other good results will follow.”