The 23-year-old Dutchman, who finished ninth overall at last year's Giro d'Italia while supporting Tom Dumoulin, has been struggling with pain and loss of power in his left leg for a number of months and was recently diagnosed with iliac artery flow limitation.
Despite posting some strong results, such as fifth at the Volta ao Algarve and ninth at Tirreno-Adriatico, physiotherapy was deemed unsuccessful and it was decided an operation would be required to fully rectify the problem.
After crashes brought a premature end to his Giro d'Italia - where he'd been drafted in late to cover for the injured Wilco Kelderman - Oomen has been booked in for surgery in six weeks' time.
"In an attempt to solve the issues we tried numerous treatments such as physical and manual therapy, alongside adjusting his position on the bike. Throughout the process he was still able to get some good results which gave us confidence towards his late call up for his role at the Giro, but after all of our conservative methods of treatment were to no prevail, we decided that surgery would be the only option to permanently solve the issue," said Team Sunweb physician Camiel Aldershof.
"It will take him a relatively long time to recover, and we already consider this season to be over to give him sufficient time to do so.”
There were high hopes for Oomen this year after the way he impressed in 2018 in what was his third season as a pro. After taking a top 10 at the Giro - while helping Dumoulin to second - he finished in the top 10 at the Tour de Suisse and Tour de Pologne.
This year he was set to make his Tour de France debut but was instead drafted into Dumoulin's Giro squad to replace Kelderman. After some promising signs in the early stage races, Oomen's progress has suffered a big setback but he hopes to come back stronger once the issue is properly addressed.
"I found out just before the Giro that I was suffering from Iliac Artery Limitation, which answered some questions that I had been having over the last couple of months about my left leg. I was still able to train well, and do decent races like in Tirreno and Algarve, but during TT’s, key moments and real high intensity efforts I suffered a lot; my leg simply wasn’t working as it should," Oomen said.
"My season is done which is mentally a big setback but the fact that the cause of the suffering has been found and hopefully will be solved is a relief. Sometimes you need to take one step back to be able to make two forward and I hope thats what I’m going to do now."
Iliac artery problems are not uncommon in professional cycling. Fabio Aru and Pauline Ferrand-Prévot have undergone surgery this year for similar issues, both spending just over two months on the sidelines.