Boeren defeated third tier side Rijnsburgse Boys 4-0 on Tuesday but the game was notable for the off-key showing of the 22-year-old.
Advocaat was at a loss to explain the poor individual performance, with the player having declared himself fit before the game but looking distinctly off the pace.
"I do not know what's going on with Wijnaldum," the former Russia, Belgium and Netherlands coach told Eredivisie Live.
"He had a little trouble with his groin, but nevertheless he had not complained that he did not want to play or that he'd prefer to rest.
"He did too little and he knows this himself."
The former Zenit trainer has led PSV to the top of the table since taking over in the summer but feels new faces are needed in January.
"I used this match to see some young players in my squad but that was not very satisfying," Advocaat said.
"It is clear that this squad is not at full strength and that we need to get some reinforcements during the winter break."