The north London team's run of wins was interrupted recently by losses to Chelsea and Manchester United but they won 1-0 against Liverpool last week, a result which kept them in the title race and lifted their spirits.
"It would have been very difficult for us to lose against Liverpool and go to Porto feeling confident," said coach Arsene Wenger.
The draw for the Champions League first knockout round could have been tougher for Arsenal, pitting them against Bayern Munich or one of the Milan giants, but Wenger said Porto could be tricky.
"Porto is a tough draw. They don't look like a prestigious team but every year they are in there and they can surprise people. They have been playing very well recently."
Porto's pedigree, which includes two European titles, has been clear in recent displays against English sides.
They lost 4-0 at the Emirates last season but then topped the group and gave United a tough time in the quarter-finals. Losses against Chelsea this season were close matches that could have ended in draws.
"Arsenal are the English team that can trouble us most. When they are well, they play a game that is hard to overcome," Porto coach Jesualdo Ferreira said.
"But their form can oscillate. On a good day we can cause them problems."
Porto are third in the domestic league, having started badly, and have struggled to replace influential midfielder Lucho Gonzalez, who was sold to Marseille.
Their 0-0 draw against Leixoes on Saturday belied a strong performance and followed a run of fluid and commanding wins.
Much of this has been thanks to Ruben Micael, a creative midfielder who has revitalised the team since joining from Nacional in January.
With skilful Argentine Belluschi and ball-winner Fernando alongside Micael, Porto have a midfield with technique and guile.
In attack, they have replaced Lisandro Lopez with another prolific goalscorer, Colombian Radamel Falcao, while Silvestre Varela is a threat on the wings. Burly Brazilian forward Hulk, suspended since December, has been called up and could come off the bench.
Arsenal have Russian striker Andrei Arshavin out with a hamstring problem and Alex Song in doubt with a knee injury.
Teams (probable):
Porto: 1-Helton; 13-Jorge Fucile, 14-Rolando, 2-Bruno Alves, 15-Alvaro Pereira; 7-Fernando Belluschi, 25-Fernando, 28-Ruben Micael; 17-Silvestre Varela, 9-Radamel Falcao, 11-Mariano Gonzalez.
Arsenal: 1-Manuel Almunia; 3-Bacary Sagna, 5-Thomas Vermaelen, 10-William Gallas, 22-Gael Clichy; 4-Cesc Fabregas, 7-Tomas Rosicky, 27-Emmanuel Eboue or 17-Alex Song, 2-Abou Diaby; 14-Theo Walcott, 52-Nicklas Bendtner.
