De Bruyne left the field in distress during Manchester City's 1-0 defeat to Chelsea in Porto, after taking a knock to the face from Antonio Rudiger.
It was confirmed on Sunday that the 29-year-old had sustained fractures to his nose and eye socket, and that seemed to cast some doubt over his participation in Euro 2020.
De Bruyne was always scheduled to meet up with the Belgium squad later due to his exploits for City, and Martinez is hopeful his star man will have recovered in time.
However, the Belgium coach did urge a cautious approach, with De Bruyne set to be closely monitored in the coming days.
"Kevin had a different programme, he was playing in the Champions League, that meant he had to join us seven days later," Martinez told a news conference.
"At the moment that programme has changed because unfortunately in those seven days he won't be able to rest and be with the family, it's going to be a period we need to monitor and do a lot of extra tests to see what his condition is.
"When I've spoken with Kevin, it has been quite positive as well. We've been very fortunate, Kevin doesn't need surgery. If he needed surgery, I think it would have been very difficult for Kevin to be part of the Euros.
"I think we're feeling the opposite now, because of the way that he's reacted, the treatment, we're feeling confident. We'll get a clear picture over the next seven days. It's one of those situations where we wish Kevin a speedy recovery just for him, but I feel positive he will be able to join us in the near future."
Asked if De Bruyne would be fit for Belgium's first game against Russia on 13 June, Martinez said: "We don't have an answer based on any medical facts.
"We're still assessing the extent of the injury and what is needed. I feel more confident now than I did after the final, that we'd be able to work in a way that we use Kevin in a cautious way, but a healthy way and hopefully we can see him on the pitch, enjoying his football."
After their meeting with Russia, Belgium faces Denmark and Finland in its other Group B fixtures. The Red Devils play Greece and Croatia in friendlies on Friday and Monday respectively.