While Kristaps Porzingis will be rehabbing his left knee, Knicks rookie point guard Frank Ntilikina also faces a vital summer. Knicks coach Jeff Hornacek said the skinny 19-year-old Frenchman will need more strength to increase his effectiveness in his sophomore campaign. Hornacek said Ntilikina would likely play in the summer league in July in Las Vegas. “With Frank, it’s just strength,’’ Hornacek said before the Knicks lost to the Warriors on Monday. “He’s 19 and he’s never been in a weight program. Our strength guys are working hard with him. He has gotten stronger. But it’s going to take him a couple of years, almost like KP. It’s going to take couple of years to get that strength. Everything becomes easier. You don’t get knocked off your spot. You can finish better. The more strength you have, the more conditioning you can do and not get tired.” During the All-Star Weekend in Los Angeles, Ntilikina was asked where he’d spend his offseason and he answered “France” — which raised some eyebrows. However, when pressed, he said he would “split time’’ and also be in New York.