After a life-saving kidney transplant, Alonzo Mourning is grateful to play basketball again. But he has regrets about doing it with the Nets.

Mourning yesterday again said he regrets signing with a Nets team that has unloaded Kenyon Martin and Kerry Kittles. But he said his feelings pale to those of Jason Kidd, whose days with the Nets almost certainly are numbered.

“You’ve got an upset captain who probably wants to be moved . . . An upset captain, the best player on the team upset, I don’t think it’s a good situation,” Mourning said on the eve of his regular-season NBA return tonight after his Dec. 19 transplant surgery. “That has me concerned about the future of this team and what direction we’re going.

“One of my main reasons for playing here was to play with Jason Kidd. Now you’ve got a guy that’s upset, has mixed feelings about coming back to play because of the changes that were made,” continued Mourning, who noted, “Would I have made the decision to come here if they would have gotten rid of K-Mart and Kerry? No, because I had a couple other options.”

And if Mourning is ticked, imagine how Kidd feels.

“I sympathize with [Kidd’s] more than my situation because he built this thing. . . . His presence changed the attitude and position of this organization. So for management and ownership to make the decisions they made with personnel, it’s kind of disheartening for a guy like Jason Kidd. I mean, hey, his efforts were just pushed to the side.”

Nets president Rod Thorn reiterated his stance of “no comment” on Mourning’s complaints.

Mourning, who signed a four-year, $22.6 million free-agent deal two summers ago, impressed in the Nets’ final preseason game. Now he is set for the next step tonight in a highly unlikely comeback, against his former team, Miami. If Shaquille O’Neal (hamstring) plays, Mourning likely will be matched up against him at times.

“I’m just looking forward to playing. I don’t care who’s out there,” Mourning said.