By Eric Thomas: In the latest boxing news, Top Rank promoter Bob Arum has decided not to pit newly crowned WBC middleweight champion Julio Cesar Chavez Jr. (43-0-1, 30 KO’s) against WBA junior middleweight champion Miguel Cotto in September. It seems that Arum has taken a good look at how poor Chavez’s defense was in his close 12 round majority decision win over Sebastian Zbik last weekend and is instead going to have Chavez Jr. go in a different direction.

Chavez Jr. also won’t be facing former WBC middleweight champion Sergio Martinez next, even though Martinez is campaigning hard to try and get that fight. Martinez would be much more dangerous for Chavez Jr. at this point and he’s simply not ready for the kind of firepower that Martinez brings to the table.

It would likely be slaughter if Arum were to put the young 25-year-old Chavez Jr. in with the power punching southpaw Martinez. Instead of those appealing but potential mismatches, Arum will likely put Chavez Jr. against his mandatory challenger, the number #1 ranked WBC contender Marco Antonio Rubio (51-5-1, 44 KO’s) next.

To be sure, this is a winnable fight for Chavez Jr. if he is able to come into the bout weighing 180 lbs or more. Having a big weight advantage over Rubio might be enough for Chavez Jr. to win a close decision. However, the bout brings a lot of danger for Chavez Jr., because Rubio is a much heavier puncher than Zbik. He’s not as fast as Zbik and doesn’t throw as many shots, but he looks to be a smarter fighter and punches with much more authority. Rubio sets traps and fights with a game plan in mind in his bouts.

He’s like a chess player with a lot of power moves. If Chavez Jr. doesn’t fix his leaky defense before a fight against Rubio, it’s very likely Chavez Jr. will suffer his first defeat. Rubio already took out previously unbeaten and highly hyped David Lemieux recently, stopping him in the 7th round last April. Rubio took Lemieux’s best shots in the first five rounds and then turned it up a gear in the 6th, hurting Lemieux and then knocking him down in the 7th.

Rubio might be too advanced for Chavez Jr. However, Arum doesn’t have a lot of options anymore now that Chavez Jr. is a title holder instead of just a contender. Chavez Jr. now has to fight serious contenders each time out instead of fringe level guys or B class fighters. This is going to be a sink or swim fight and a much different challenge for Chavez Jr. compared to his fight against the soft hitting Zbik. Rubio hits a lot harder and fights with much more ring intelligence than Zbik.