Catania have rejected a move from Fulham for Lopez.
Lopez will move to AC Milan if the Rossoneri fail to sign Carlos Tevez from Manchester City.
"We have an agreement with AC Milan, but it is a timeshare arrangement: Milan have blocked Maxi Lopez, and we said no to the offer of Fulham," Catania's chief executive Pietro Lo Monaco told the Gazzetta dello Sport.
"Now we are waiting for the Rossoneri, which must solve a something [Tevez's deal].
"The agreement has been in place for some weeks and at this point it may well be that Maxi plays the next game with AC Milan."
He added to Sky Italia: "Maxi Lopez is virtually a Milan player, we made the player content."
"There is an agreement with Catania: if Tevez won't come, Maxi Lopez arrives," said AC Milan chief Adriano Galliani.
"Now let's see what happens, we'll wait a few more days. Maxi Lopez is a player who interests us very much, we already agree with everything and therefore he is very likely to arrive.
"The desire of Tevez to come to AC Milan is very pleassing, and we also want him to arrive. Let's see."