Today, more than 40% of acute ischemic stroke (AIS) patients treated with endovascular therapy (EVT) will remain severely disabled at 3 months. The inventors hypothesized that acute microglial inflammation plays a pivotal role in post-AIS brain changes leading to poor functional outcome. Glycoprotein YKL-40 is a biomarker of astrocytic and microglial activation. The inventors thus conducted a monocentric prospective study including 120 patients treated with EVT, for whom 3 blood samples (before, within 1-h, 24-h post-EVT) were drawn to measure plasma YKL-40 concentrations. The inventors found that 3-month functional outcome was significantly and independently associated with acute plasma YKL-40 levels. the present invention relates to the use of YKL-40 as a biomarker for assessing functional outcome in AIS patients treated with EVT.