If the Knicks expect center Jahlil Okafor or point guard D’Angelo Russell to fall into their laps with the fourth pick in the NBA draft, they should think again.

According to a league source, the Sixers, who pick third, still have a firm Big 3 of Karl-Anthony Towns, Russell and Okafor and won’t let any of the trio slip to Phil Jackson. Despite their young, marquee depth up front, the Sixers would take Okafor even if it’s to collect an asset to trade later.

Speculation that Russell is trying to avoid being picked by the moribund Sixers escalated when he canceled workouts with them this weekend. There also were rumblings that perhaps the Lakers, after working Russell out, had given the Ohio State combo guard a guarantee at No. 2. The Philadelphia Inquirer reported he was just “real sick’’ and a Sixers workout could be rescheduled. Russell has told reporters he also has agreed to work out for the Knicks.

Even if the Lakers gave Russell an endorsement and Okafor is dangling at No. 3, the Sixers, as of now, would choose him over the flavor of the day, 7-foot-1, 220-pound power forward Kristaps Porzingis, the young Spanish leaguer who reportedly dazzled at his only pre-draft workout in Las Vegas on Friday.

Point guard Emmanuel Mudiay has not yet worked out for the Sixers, but he would have to be superb, because many league executives are concerned with the level of competition in the Chinese Basketball Association, where he most recently played.

Jackson and coach Derek Fisher were at the Porzingis workout, but it’s also a long shot for the Knicks to take the Latvian sharpshooter. They are trying to increase their defensive grit this offseason and not so much worrying about shooters in the triangle offense.

Still, Porzingis reportedly made shot after shot and a series of dunks in the workout, put on by agent Andy Miller. He has drawn comparisons as a future Dirk Nowitzki at best, Danilo Gallinari at worst.

“The body’s a long way off so he’s couple of years away from impact,’’ one NBA scout said. “He’s going to look great in a workout but he’s a young European who hasn’t played much. Too much risk at [No.] 4 for the Knicks.’’

Many NBA personnel men can see the Knicks taking the surer bet in Duke freshman swingman Justise Winslow over Mudiay at No. 4 because of his championship pedigree, defensive knowhow and ability to play shooting guard and complement Carmelo Anthony, an acquaintance. Kentucky’s sophomore defensive big man Willie Cauley-Stein is considered the wild-card pick.