Porto's high-scoring attack could be missing its biggest weapon for Wednesday's match against Liverpool in the last 16 of the Champions League.
Cameroon forward Vincent Aboubakar didn't practice with the rest of the squad on Tuesday because of a lingering muscle injury and remains doubtful for the first leg at Estadio do Dragao.
He hasn't played in the last two matches for the Portuguese league leaders, missing the derby against Sporting Lisbon in the Portuguese Cup and the league match at Chaves.
The 26-year-old Aboubakar has been in relentless scoring form this season, netting 20 goals in 28 matches, including five of the team's 15 goals in the group stage of the Champions League.