The Knicks should officially add free agent reserve shooting guard J.R. Smith to Linsanity today, making the hottest team in the NBA a deep team as well.

According to multiple sources, Smith, who played in China during the lockout and became eligible to sign an NBA deal on Wednesday, will be at Madison Square Garden tonight, but won’t make his debut until Sunday against the Mavericks.

The Knicks have to cut a player to make room for Smith and Renaldo Balkman, who has been out of the rotation since early January, is the expected candidate, according to a source. Coach Mike D’Antoni was never a big fan of Balkman, a throw-in to the trade with the Nuggets for Carmelo Anthony. Balkman has one remaining year at $1.8 million and could have been an amnesty casualty if the Knicks were still going for 2012 cap space.

The only potential delay for the Smith signing is if the Knicks attempt to buy out Tony Douglas’ contract.

Ironically, if Smith had been eligible to be signed two weeks ago, the Knicks probably would have cut Jeremy Lin for financial reasons because his contract wasn’t guaranteed and he hadn’t convinced D’Antoni he belonged in the mix.

The Knicks pursued Smith for a couple of weeks and D’Antoni said they would be “very aggressive’’ in offering their $2.5 million cap room exception on him as they were looking to add his 3-point shooting ability.

Even their seven-game win streak and perfect chemistry created by the stunning emergence of Lin didn’t sway the Knicks from going after Smith, though it could be seen as a risky move because of his reputation as being a rabble-rouser. But Anthony, who has the same agent as Smith, recently endorsed the move.

Smith, a former star at St. Benedict’s Prep in Newark, can be an explosive scorer and deepens the Knicks’ backcourt depth, especially if point guard Baron Davis never makes it back. Landry Fields is red-hot and not in danger of losing his starting shooting guard slot.

If Davis comes back after the All-Star Break, the Knicks could have a very deep backcourt of Iman Shumpert, Davis and Smith.

* Celtics broadcaster and former player Cedric Maxwell is not sold on Lin.

“Now let’s not get crazy, OK,’’ he said on Boston radio. “It’s been [seven] games. That does not make the season. I know that this is a wonderful story … Call me back in about two months. Because some of the team he’s played against so far have not had dominant point guards.