The 26-year old Brazilian arrived on a loan deal from Brazilian club Corinthians last month but has not played for some time and is busy ramping up his fitness in a bid to be conditioned for first-team action for the February 27 league meeting with Southampton.
"I'm happy with his development," Hiddink said.
"He played his last game on the 28 November.
"Then they were on holiday ahead of the new season.
"So he's in pre-season now."
The Dutchman claims that the Sunday's FA Cup clash with Manchester City will come too soon for the Brazilian.
"You need at least four to five weeks in pre-season to get [Pato] top fit," Hiddink added.
"He's not yet fully game fit, but he's in the third week of preparations.
"I hope, after this weekend, he'll be in shape where we can go with him."