Online gambling has significantly altered the situational and structural characteristics of gambling products, to the extent that online gamblers might be substantially different from traditional offline gamblers. A growing body of literature has identified the evolving features of online gambling and the individuals who engage in it. However, beyond understanding the individual characteristics of this subgroup, relatively less effort has been made to examine whether existing cognitive-behavioural therapy (CBT) approaches are still entirely relevant for online problem gamblers, or whether changes are needed to adapt according to gambling mode of access. To understand what kind of challenges online gambling poses to mental health professionals dealing with disordered gamblers, four focus groups comprising 28 Spanish participants were carried out. All the treatment providers had ongoing experience with online gamblers undergoing treatment, and included clinical psychologists, mental health social workers, and a medical doctor. The data were examined using thematic analysis. The analysis identified five main themes that characterised online gamblers: (1) being of younger age, (2) lack of conflicts at home and at work/educational centre, rarely presenting violent or aggressive behaviour, (3) gambling disorder only being identified by overdue debt, (4) co-occurring conditions with technology-related abuse rather than other substance-related addictions, and (5) skill-based gambling. The study highlights mental health workers’ perceived insecurities about how to best treat online gamblers, and discusses the specific characteristics that CBT for gambling disorder might need to incorporate to adjust for this particular group of gamblers.