Arsenal captain Cesc Fabregas limped off the field with a hamstring problem after scoring the first goal against Burnley on Saturday.
Fabregas had a similar problem in the early part of the season, but even then Wenger was forced to play him against Aston Villa knowing that he could aggravate his hamstring.
Eventually, the Spaniard won the match for Arsenal, but did aggravate the injury, forcing him out for the next three weeks to aid his recovery.
Now, Wenger faces a similar dilemma ahead of the Porto clash. "I am ready to take the gamble. But if there is more than a 50 percent chance of his hamstring going I will not take it," said Wenger.
Fabregas is very crucial for Arsenal in the big games. He's been in scintillating form so far this season and it would be a huge setback for Arsenal to lose him at the end of the season.
At the business end of the season, one would expect the best players to take part. Arsenal has more than a realistic chance of winning the League, but without Fabregas it would be highly unlikely.
However, with a place in the quarterfinals of the Champions League at stake, Wenger might risk playing Fabregas knowing that further damage to the hamstring could end the season for the Arsenal captain.
It's a difficult situation for Wenger.
In a must win game, Arsenal have to overturn the 2-1 deficit that they suffered in the first leg at Porto. But, without the talismanic midfielder, is it possible against a highly motivated Porto side?
On the other hand, Samir Nasri looks to be in good form. He had a noteworthy outing against Burnley and dominated the Burnley defense at will.
He plays much like Fabregas, and he's already showed his potential against Burnley when the Arsenal captain departed due to injury. He carried the entire team on his young shoulders.
But, Porto is no Burnley. They're a dangerous side. They're more physical and are brave enough to attack.
It's a huge decision for Wenger to make.
I feel it would be better to rest Fabregas, especially when Andrei Arshavin, Alex Song, and Abou Diaby are set to feature in the starting line-up. Nasri has impressed enough to play more at the attacking midfield position rather than on the flanks.
Is it worth the risk playing Fabregas (knowing that further aggravation of his hamstring may well rule him out for the rest of the season), when you've a similar player like Nasri?