The 27-year-old striker has been out for just over three weeks with a thigh injury but resumed full training on Wednesday.
But Ranieri admitted he is worried the Colombia international may be lacking fitness after interrupted training over the past month.
"I will have to think about (if Falcao will play) - I want to decide later," Ranieri said.
"He can play but I have to take into consideration that he hasn't trained for a month.
"I don't know what would be reasonable, but I have to think it through and then decide."
The Italian tactician urged focus ahead of Friday's Ligue 1 fixture and banished thoughts of surpassing Monaco's highest-ever points tally at the halfway mark in the season.
"Valenciennes play well, they press high up the pitch, they are quite compact," Ranieri said.
"We must be intelligent and motivated - it's important to win this game but it will not be easy."
Eric Abidal echoed Ranieri's sentiments, with the defender maintaining that the team were focused on the match despite the looming prospect of the Ligue 1 break.
"The game against Valenciennes will be the last before the break and it's important to finish on a strong note," Abidal said.
"We don't have to think about the holidays and as said the coach in the changing room, we are professionals and we have to stay focused until the end.
"For the group and for the club it is important to finish with a good result."
