Rob Kardashian is purportedly determined to make a 2015 comeback, and his former brother-in-law, Lamar Odom, has reportedly offered to guide him into his road back to fitness.

According to reports, Lamar Odom also wants to get back into his NBA physique before 2015 ends, and he's allegedly encouraging Rob Kardashian to take the challenge with him.

"Lamar and Rob had a special bond when Lamar was married to Khloe and Rob was crushed when they got divorced, but that brotherly love never went away," an insider told Dish Nation.

According to the insider, Rob Kardashian's sister and Lamar Odom's ex-wife, Khloe Kardashian, approves of the former NBA player's idea.

After all, both Rob Kardashian and Lamar Odom have been through a lot these past few years, and 2015 could be the year they both get up from the slump.

"Khloe is 100 percent on board with Lamar's plan. She adores her brother and knows how much he loved Lamar," the source added.

Rob Kardashian has been avoiding the public eye amid purportedly suffering from depression and weight gain. The only Kardashian brother reportedly chose to stop participating in his family's reality show, "Keeping Up With The Kardashians." He has also missed a lot of family events including Kim Kardashian's wedding to Kanye West.

Apparently, Rob missed yet another 2015 Kardashian-Jenner shindig this week - Kylie Jenner's birthday party.

"Rob was obviously invited but chose not to attend," Dish Nation's source said. "He's not committed to the gym yet and he has no plans of making any public appearances until he's back in shape."

According to another source, Rob just couldn't bring himself to consider going to Kylie Jenner's birthday party.

Kylie Jenner has been trying to make a name for herself in the entertainment industry, and Rob allegedly knew that her birthday had the potential to be a celebrity circus.

"With the way he feels about himself at the moment, the last thing he wanted to do was to go to Nobu in Malibu, a spot where the paparazzi camp out waiting for celebrities to arrive,"a source told Hollywood Life.