Joao Fonseca on Buenos Aires upset, chronic back condition: “My body wasn’t helping me”

One year after his first major ATP breakthrough—winning the IEB+ Argentina Open title at just 18—Joao Fonseca returned to the Buenos Aires clay and suffered his first big heartbreak in the city.

Fonseca, the defending champion and No. 3 seed at the ATP 250 event, fell in the second round to Alejandro Tabilo, 6-3, 3-6, 7-5 on Wednesday. The defeat marked his third consecutive loss and raised fresh concerns about his physical condition.

Read More: Joao Fonseca delays 2026 debut, withdraws from Brisbane with lower back injury

“If I say no, I’d be lying, so yes, I certainly felt a bit more pressure,” the 2025 champion admitted in his post-match press conference, according to Punto De Break.

“I felt tense from the beginning of the match. I tried to bring intensity, motivation, eagerness, even sought support from the crowd, but it wasn’t my day. There was a lack of conviction and confidence…”

“I tried everything to motivate myself,” he added. “I was pissed off with my legs, which weren’t moving the way they needed to. My body wasn’t helping me hit the good shots I wanted.”

A lower back injury affected Fonseca at the end of last season, and there were signs the lingering issue remained a factor in 2026. He withdrew from his scheduled Australian Open tune-up events in Brisbane and Adelaide, and later fell in the first round in Melbourne to rising American Eliot Spizzirri in four sets.

“I was born with a back problem and suffered a stress fracture five years ago,” he told Brazilian press after pulling out from Brisbane. “Some days I feel more pain than others. It’s an injury that never fully disappears, but one I have to learn to manage day to day.

“Over the last few days, I’ve felt like I was improving a bit, but it’s hard to say if I’ll be at 100 percent.”

According to his team, the chronic condition is called lumbar hypolordosis—also known as “flatback syndrome,” a condition in which the lower back has lost its natural curvature.

“João has a straightened spine and suffered a stress fracture five years ago, when he was still a juvenile. Thus, the lower back is the most sensitive area of his body and, because he is a high-performance athlete, it requires constant care,” says a statement provided to GE (Globo Sports).

“Soon, João will be back to the tournaments, 100 percent recovered. The mentality of the team is always to preserve the athlete’s health, aiming for a long-term career.”

Low back conditions are common among athletes. More widely known is “swayback” (lumbar hyperlordosis), an exaggerated arch in the lower spine that can cause progressive pain. Similarly, “flatback” syndrome can affect mobility and flexibility, making athletes more susceptible to long-term pain and secondary injuries as other parts of the spine compensate for the imbalance. In more advanced cases, it can contribute to disc degeneration and even compression fractures.

Treatment typically includes physical therapy, anti-inflammatory medications and injections, and pain management programs aimed at improving posture and controlling symptoms.

“I tried everything to motivate myself. I was pissed off with my legs, which weren’t moving the way they needed to. My body wasn’t helping me hit the good shots I wanted.”

For now, it’s back to the drawing board as Fonseca turns his attention to Rio de Janeiro, where the ATP 500 Rio Open will be contested on home soil.

“They say ‘Joao is going to be the next Guga, the next Alcaraz’, I’m writing my own story and doing everything at my own pace,” Fonseca said. “What I can do on my part is work really hard on my mentality and my physique.”

The Rio Open presented by Claro takes place February 16–22, 2026, and also features Francisco Cerundolo, Matteo Berrettini and Gael Monfils at the Jockey Club Brasileiro.