Mawson is under consideration for the World Cup by England coach Gareth Southgate.
"He is one of the best central defenders in the Premier League," Swansea manager Carvalhal said ahead of his side's crunch trip to Brighton on Saturday.
"He is progressing a lot since I arrived at the club.
"One of the best English centre-backs? I'm absolutely sure, but it's not my job to say whether he deserves to go with the national team.
"It is the same if someone asked me about a player from another team.
"I understand he is English, but I don't want to give an opinion and interfere with what my colleague (Southgate) wants to do."