Groves will put his WBA super-middleweight title on the line against IBO champion Eubank on February 17, with the bout generally regarded as the biggest all-British clash of the last 12 months.
However, ahead of the second defence of his world crown, Groves has suggested that Eubank is "not good enough" to compete at world level at 168lbs.
The 29-year-old told reporters: "I'm sorry to say that Junior isn't good enough, he doesn't have the pedigree or the ability. You're Insta-famous. Fantastic short clips on the bag or pads. They look great. You punch from the ankles from the get go.
"Junior's been craving the big fights without actually wanting them. He attaches his name to big fights and then they fall through and he boxes at a much lower level."