Fernandes made his debut for the club, starting the whole game, in a 3–0 win against TuS Erndtebrück in the first round of the DFB–Pokal. He then appeared in the first two months for the Eintracht Frankfurt, playing in the midfield position. However, Fernandes tore his hamstring during a match against RB Leipzig on 23 September 2017 and was substituted in the 27th minutes, as the club lost 2–1. Following this, it was announced he would be out for several weeks with a hamstring injury and didn't play for two months. It wasn't until on 15 November 2017 when Fernandes returned to the first team, coming on as a 75th minute substitute, in a 1–1 draw against TSG 1899 Hoffenheim. Since returning to the first team from injury, he, however, found himself in and out of the starting line–up for Eintracht Frankfurt. In the semi–finals of the DFB–Pokal against Schalke 04, Fernandes was sent–off for a straight red card, having come on as a substitute bench three minutes before, as the club won 1–0 to advance to the next round. He watched from the sidelined, as Eintracht Frankfurt won 3–1 against Bayern Munich to advance to the next round. At the end of the 2017–18 season, Fernandes went on to make twenty–two appearances in all competitions.