The Bobcats announced that Clifford underwent a successful procedure Friday to have two stents placed in his heart.
Bobcats president of basketball operations Rod Higgins said in release Friday that Clifford is "resting comfortably" in the hospital but it's too early to know when he'll return to work.
With Clifford unavailable, Ewing, the Bobcats' associate head coach, took the reigns.
"It's definitely not the way I wanted to start my head-coaching career with him being in the hospital," Ewing said before the game.
Ex-Knicks coach and current ESPN NBA analyst Jeff Van Gundy and Bobcats executive Michael Jordan reached out to Ewing to offer advice.
"[Jordan] called me and told me if I don't win I'm fired," Ewing joked. "He said it's very ironic that my first opportunity to be a head coach is against the Knicks."
Ewing was passed over several times for assistant and head coaching jobs by New York after his 17-year playing career.
The Knicks made Ewing an offer to coach the team's D-League affiliate, the Erie BayHawks, last season but Ewing declined because he wanted to remain in the NBA, according to a source.
"I don't even worry about that. All I worry about is getting our team ready, getting our team focused," Ewing said on Friday. "Not many (Bobcats players) know that Cliff is not going to be coaching tonight. I have to relay that to them.
"Apart from all that stuff, I’m happy with the Knicks, I’m happy with (Knicks owner and MSG chairman James) Dolan."
Ewing admitted to being "nervous" early in the game on Friday but said he was later "able to calm down and do my thing."
His Bobcats struggled to defend the three point shot (New York hit 46 percent of his attempts) and couldn't contain Bargnani. The seven-footer had his best night as a Knick on Friday.
"We cut their lead but it wasn't enough," Ewing said. "(Bargnani) just made some shots."
It's unclear at this point when Clifford will return. Ewing hopes Clifford will be back on the bench Sunday. The Bobcats next play on Monday at home against the Hawks.