The Belgian, riding in his first season at WorldTour level, had enjoyed an impressive spring, with third in Dwars Door Vlaanderen and fourth in a highly competitive Scheldeprijs.
Further success followed at the Baloise Belgium Tour, with the Trek-Segafredo hierarchy witnessing enough to bring the 25-year-old to his first Grand Départ. The decision was vindicated with a couple of top ten places during the opening week but, on the stage 13 time trial, Theuns' world came crashing down when he fell on a descent and suffered a compressed fracture of the T12 vertebra.
From the images of the fall it was clear that the Belgian was in a serious state and the team quickly confirmed that his season was over.
At the Trek-Segafredo camp in Spain this week a cheerful Theuns sits down in the lobby of a plush hotel. The worst is certainly behind him but his comeback is still very much going through the gears, as he explains to Cyclingnews.
"I'm doing better than I'd expected. I can train to a schedule and the only thing I have to watch out for is power training. I still have to do specific training for my back and still have some pain and feel it from time to time but it's okay," he says after enjoying a morning spin with his teammates.
This feels like a world away from where Theuns laid mid-July.
"I was scared, of course. I’d studied physiotherapy and although I'd never broken my back before I knew that there was something wrong. It was so scary because an injury to the vertebrae can be really serious. I was just happy that in the first moments I had the team with me.
"Then my girlfriend came and she spent the night at the hospital. That really helped because it was such a hard moment for me and it felt like there was so much coming at me all at once."
Back surgery soon followed, along with a further week in bed. When he could finally leave hospital Theuns was forced to re-model part of his house in an attempt to avoid movement and climbing stairs. He lived on the ground floor and wore a brace for three long months as part of his rehabilitation, as his girlfriend and family rallied about him.
"Hospital was a huge shock for my body and when I started walking it was so strange. Then at the beginning I had the brace and it gave me good support but after a few weeks I was really sick of it."
Baby steps were required at first and Theuns spent five days a week in lengthy physiotherapy sessions as summer turned to autumn, autumn into winter. He kept in touch with teammates as they trotted over the globe from race to race, as he traded Grand Tours for stretching and strength work.
'That first ride was incredible'
Finally, although still with the use of the brace, he was able to throw his leg over a saddle for the first time since the crash. He began to cycle to the therapy appointments and, although the distances were short, they were a huge mental breakthrough for the rider.
"It was only 7km but that first ride was incredible," says Theuns. "One minute you're in the Tour de France, then you're having surgery in the blink of an eye, so to be back on the bike felt like a really great moment.
"Up until that point I had to ask my girlfriend to bring me everywhere and I needed people for everything. Being back on the bike was a huge difference. Just simple things like going out for a coffee was a huge step. At the start of my recovery I wasn't even washing myself or doing my shoelaces.
"The doctors said it would be a three to six month recovery but that just covered getting back to normal life. It didn't cover racing and for me it took longer because if you're a sportsperson it's really hard to just do nothing. You can do it for a month but any longer and it's really hard. At the same time I knew that I couldn't push things too hard."
Theuns is very much aware that his patient approach must remain in place and that he cannot afford to take any risks over the next few weeks and months. The screws from his operation are still in place and he is under strict instructions not to ride over cobbles until January – a slight problem perhaps given his home is in Belgium – but for now the Classics rider is just appreciative of the support network around him and that he has made it back.
He has raced two editions of the Revolution Series and his road programme will soon take shape but those baby steps still remain.
"I felt some pain after those track races but the day after I felt even better. I think the race was good for me because I wasnlt focussing on my back but just racing. It was more natural and I think since then my back is a lot more mobile.
"I feel maybe better than last year in terms of fitness, but it's hard to say where I am for things like power and sprints. I'll learn more after the first few races, and if there's a limit on my performance. After the second Revolution race I felt for the first time that I could come back to the top level. Before that I had my doubts."
Theuns has come along way in the last few months. There's no doubt that if he keeps moving in the same direction he'll return to where he was earlier this year.