Belgium captain Hazard has not played since fracturing his right ankle on international duty in May, and has only just made a comeback to training with the Premier League champions.
He is unlikely to play any part in Sunday's fixture against Everton before heading on international duty, but Martinez says Hazard's standing as captain was a key factor in his decision to call on the 26-year-old.
"I think the selection [of Hazard] is to see how he is," Martinez told a media conference. "It does not mean he is fully fit, we will make a decision on that on Monday.
"Eden is our captain and needs to be in our selection. He is in a good moment, he is coming back from injury with really good signs. The information we have was good enough to call him up.
"We have got a very good relationship with Chelsea, everything has been open and honest.
"We need Eden Hazard as a footballer, but as a human being as well, there has been no conflict with anyone.
"It is important we started with Eden in the squad."
Chelsea coach Antonio Conte was surprised by the decision, though, and believes the attacker is not ready to return to action.
"I'm a bit surprised by this decision," Conte told a news conference ahead of Sunday's league game at home to Everton.
"I was a coach of the national team with Italy but I respect the decision of the other coach.
"If Hazard is fit, then he can play [for Belgium]. [But] if [he] is ready, why does he not play with us?
"I hope after the international break to have the whole team [fit] and to think about Hazard.
"I see him every day. It's very important to give him the right time to recover very well. He's an important player for us."
Radja Nainggolan's omission has raised eyebrows. The Roma midfielder has played only four times for his country under Martinez and misses out altogether this time.
In his stead, Steven Defour is offered a recall for the first time since November 2016, while Jordan Lukaku's reward for a fine start to the season at Lazio is his first call-up in 10 months.
Belgium host Gibraltar on Thursday, before travelling to Greece three days later as they look to maintain their unbeaten start in Group H.
Belgium squad in full:
Defenders: Toby Alderweireld (Tottenham), Laurent Ciman (Montreal Impact), Leander Dendoncker (Anderlecht), Vincent Kompany (Manchester City), Jordan Lukaku (Lazio), Thomas Meunier (Paris Saint-Germain), Thomas Vermaelen (Barcelona), Jan Vertonghen (Tottenham)
Midfielders: Nacer Chadli (West Brom), Kevin De Bruyne (Manchester City), Steven Defour (Burnley), Mousa Dembele (Tottenham), Marouane Fellaini (Manchester United), Youri Tielemans (Monaco), Axel Witsel (Tianjin Quanjian)
Forwards: Michy Batshuayi (Chelsea), Christian Benteke (Crystal Palace), Yannick Carrasco (Atletico Madrid), Eden Hazard (Chelsea), Thorgan Hazard (Borussia Monchengladbach), Romelu Lukaku (Manchester United), Dries Mertens (Napoli), Kevin Mirallas (Everton), Divock Origi (Liverpool)