The Portuguese winger has found first-team opportunities at Hillsborough limited, mainly due to injury, and had only made three substitute appearances all season.
Last season he only played twice with the second game – a home defeat to Fulham – cut short due to a red card.
But he was a surprise starter in Wednesday’s 2-2 draw with Hull City three days ago.
The 28-year-old struggled to make an impact and was replaced at half-time with the Owls trailing 1-0, but Carvalhal said Matias had earned his start after impressing in training.
“It wasn’t easy for Marco,” said Carvalhal. “He deserved his place because he has been training really well. He is a nice guy.
“He almost played in the last game (at Reading), if we had decided to play 4-3-3. But when we decided to play 4-4-2, that’s why he didn’t play.
“The game was not easy for him in the first half.
“The dynamic, they closed the spaces, so when the opposition are very compact let’s use a different approach.
“We took a lot of risks. We had three attackers, two attacking midfielders, when the opposition play counter-attack – and have fast players – they can get a second goal.
“It’s our lives, we take the risks and we can win.”
Wednesday’s owner Dejphon Chansiri is resigned to losing hot prospect George Hirst, the reported subject of bids from Leeds United and Premier League duo Leicester City and Everton.
The striker – whose contract expires in the summer – has not played at any level for the Owls this season because of a contract dispute. His only outings have come with the England Under-19s.
Chansiri said: “As far as we are concerned, we have tried our best and we are disappointed, but it seems there is little more we can do to keep George at Sheffield Wednesday.
“Ultimately, we are a team on and off the pitch, we all help each other. If we allow an agent or adviser to disturb what we have in place then they will be bigger than the club, which will never happen under my chairmanship.”
Owls defender Tom Lees, 26, faces six weeks out after undergoing groin surgery.