It is not the first time that the 28-year-old has faced questions over his weight.
He picked up an untimely knock after arriving at Santiago Bernabeu, preventing him from making the impact he had been acquired to deliver.
A slow start has since been made to his time with the Blancos, leading to more criticism regarding his fitness.
Martinez, though, considers a talismanic presence for his country to be in fine shape and remains puzzled as to why detractors are so quick to pick at a forward who has proven himself several times over.
The Belgium head coach said when quizzed on Hazard: "I'm happy to see Eden with the group.
"He's smiling. He's a world-class player, who is unique, talented.
"He is also very professional and, although he has already won trophies [in his career], he is reaching the highest point of his career.
"He takes great care of himself and, in my eyes, he's not fat."
Another star turn for Belgium and Madrid to have faced questions regarding their contribution at club level is Thibaut Courtois.
The 27-year-old goalkeeper is still searching for consistency and full match sharpness.
Illness has been doing his cause few favours of late, with a stomach problem forcing him off during a Champions League clash with Club Brugge and out of a La Liga meeting with Granada.
Courtois is, however, part of the latest Belgium squad and will be pushing for a starting berth against San Marino on Thursday.
Martinez added: "Courtois, when he arrived, had lost two kilos.
"He'd suffered from a serious bowel problem and therefore needed time to recover.
"Now he's back and is in top shape."
Belgium currently sit top of Euro 2020 qualifying Group I.
Maximum points have been taken from six games so far, with qualification all but secured.
They beat San Marino 4-0 in their previous meeting back in September and will be expecting the goals to flow once more when on home soil.
It could be that Hazard has a role to play in midweek, with the talented forward looking to build on the effort he registered against Granada which opened his account for Madrid.