On 12 August, he made his official debut for Sporting netting the winning goal against archrivals Porto in a 1–0 home victory. Following his goal against Porto, shirt sales featuring Niculae's name and number went crazy making an income of nearly $65,000 that day. He received his first red card of his career next round, in a 0–3 away defeat against Belenenses, missing also a penalty in the process. He returned on the field following his one-match ban on 8 September, winning a penalty that gave Sporting a 1–0 lead against Leiria, after Mário Jardel converted from the spot. Eight days later, he scored a brace and won a penalty in a 3–1 win against Gil Vicente. On 1 October, Niculae scored Sporting's second in a 5–0 victory over Vitória Guimarães. On 18 October, he scored his first European goal, netting the only goal in a 1–0 win against Halmstad in UEFA Cup. On 27 October, Niculae scored another brace giving his team an easy 6–0 win, the first away win for Sporting to score six goals since 1994–95 season. Five days later, he scored again in UEFA Cup in the second leg against Halmstads, in a 6–1 victory. On 5 November, he netted again in a 5–1 win against Salgueiros. Following his excellent start for Sporting, the club set Marius Niculae a release clause of €17,500,000. On 6 December, he scored his third goal in UEFA Cup, in a 1–1 home draw against Milan. On 17 December, he finished second on the vote for "Gazeta Sporturilor's" Romanian Footballer of the Year Award, behind Cosmin Contra. On 22 December, in a game against Vitória de Setúbal, after a dangerous challenge, he suffered a career-threatening knee injury ending his season prematurely. Despite László Bölöni intended to give Niculae his come-back on the field faster than anticipated on Sporting's last game of the season against Beira-Mar, the doctors eventually denied the player to return. The "Lions" won the double, Niculae contributing with seven goals in 16 games in the league, while in the cup he played only in a 3–1 win against Vilanovense.