Kevin De Bruyne's goal could prove costly for Napoli despite it setting the defending champions on the way to a 3-1 win over Inter Milan and back to the top of Serie A on Saturday.
De Bruyne appeared to pull a muscle as he converted a first-half penalty, immediately clutching the back of his right thigh. The former Manchester City player looked distraught and had to be helped off the field by two medical staff.
Scott McTominay and Frank Anguissa also scored for Napoli after the break, either side of an Inter penalty converted by Hakan Çalhanoğlu.
The result got Napoli back to winning ways -- after last weekend's loss at Torino and Tuesday's chastening 6-2 defeat at PSV Eindhoven in the Champions League -- and lifted them a point above second-placed AC Milan, who drew against Pisa on Friday.
"I live the game with my players, for better or for worse," said Napoli coach Antonio Conte, who also steered Inter to the title in 2021. "We won despite the difficulties, we have important players absent and now De Bruyne has also been injured. Let's say it's not a very lucky year, maybe someone has cursed us."
Inter, who had been on a seven-match winning run, were left in fourth.
"Inter had come to kill us, they were coming off a great moment, while we were in difficulty," Conte added. "But we have no intention of dying and we played a tough and vigorous match, putting in an excellent performance despite the difficulties."
Napoli were already struggling with injuries and their problems got worse when De Bruyne was forced off after firing his spot-kick powerfully into the bottom corner.
The penalty had been awarded after Inter midfielder Henrikh Mkhitaryan was adjudged to have fouled Giovanni Di Lorenzo. Mkhitaryan also went off injured.
Inter came close to levelling the match in the dying seconds of the first half as Alessandro Bastoni hit the crossbar and Denzel Dumfries clipped the post.
The visitors continued to pour forward after the break but McTominay doubled Napoli's lead in the 54th minute following a rapid counterattack. He sprung the offside trap to run onto Leonardo Spinazzola's fine pass and drive it into the bottom corner from the edge of the area.
It was McTominay's third goal this week after his brace against PSV.
Çalhanoğlu reduced the deficit five minutes later with a penalty after Napoli defender Alessandro Buongiorno charged down a Lautaro Martínez header with his arm.
However, Anguissa restored Napoli's two-goal advantage in the 67th when he finished off another clinical counterattack.