FC Porto come into the second leg of their Champions League last-16 tie with Swiss champions Basel on Tuesday with the upper hand but with serious concerns over the fitness of their leading scorer.

The Portuguese club have the edge in the tie after a 1-1 draw in Switzerland in the first leg last month but were dealt a potentially serious blow when Jackson Martinez came off with a thigh injury in Friday's 1-0 win at Braga that could keep him out for up to three weeks.

The Colombian star has scored 17 goals in the Portuguese league this season and six times on Porto's run in the Champions League, so it is little wonder that the Dragons are sweating on his fitness.

"We are talking about a player who is mentioned for his goals but he is about so much more than that. He is an example to everyone for his character and his professionalism," said coach Julen Lopetegui, who has Cameroon forward Vincent Aboubakar waiting in the wings after he came off the bench against Braga.

"If he came off it wasn't for nothing. The squad needs to be ready and Aboubakar gave a good response."

However, Porto's outstanding performer in recent weeks has been the Spanish winger Cristian Tello, who got the winner at Braga after netting a hat-trick in the previous week's defeat of Sporting Lisbon.

The two-time European champions are aiming to return to the quarter-finals of the Champions League for the first time since 2009, when they were eliminated by a Cristiano Ronaldo-inspired Manchester United.

Porto came from behind to draw with Basel at the St Jakob-Park as a Danilo penalty cancelled out Derlis Gonzalez's opener for the Swiss side.

The match will be a special occasion for Basel's Portuguese coach Paulo Sousa, who came up against Porto as a player for Lisbon giants Benfica and Sporting.

He is hoping to lead Basel into the last eight in Europe's elite club competition for just the second time, with their previous appearance ending in a 6-5 aggregate loss to Celtic in 1974.

Basel are without the suspended Marek Suchy but their man to watch should be striker Shkelzen Gashi, who is the top scorer in the Swiss league with 16 goals, including a brace in the 3-0 weekend win against FC Thun.