The 26-year-old, who is on loan at the Liberty Stadium from Villarreal, scored twice in Swansea's 3-0 victory over Norwich City on Saturday.
"He was our best player," Monk told ITV Sport. "He typified everything that I asked of the team for this week - not just on the ball, but off the ball.
"The two goals that he got were special and very good finishes and he showed another string to his bow - that he can be asked to play in other positions.
"I think if he continues to play like that he'll give himself a very good chance of getting in the World Cup squad."
De Guzman has won eight international caps.