The striker is serving a three-match domestic ban for a straight red card picked up against Swansea last month, but he is free to play in the Champions League.
"Fernando is keeping fit in training and he also will be almost a month without playing for us in the Premier League, so I will decide in the next couple of days whether to use him on Wednesday," said Chelsea boss Andre Villas-Boas.
"We cannot allow ourselves to relax against Genk but that is what can happen in a game which everyone expects you to win.
"Our group is still very open so we have to concentrate on taking six points from our next two games against Genk to put us in a good position to qualify for the next round."
The Spanish international has scored just three Premier League goals for Chelsea since signing from Liverpool for a reported fee of £50m in January 2011.