"I feel bad for Clint," Coughlin said.
Sintim suffered the season-ending injuries during the third quarter of Thursday night's preseason game against the New England Patriots as he was trying to make an open-field tackle. During the play, Sintim's knee bent awkwardly, causing him to go down. He was helped off the field and couldn't put any pressure on his right leg.
"I knew as soon as I hit. ... It's unfortunate," a choked-up Sintim said afterward. "I worked really hard to get back. It's just unfortunate but that's the way football is. I'm going to give myself a couple of days and get back on the grind."
The third-year pro, who was selected by the Giants in the second round of the 2009 draft, tore his right ACL last December. He was serving as Mathias Kiwanuka's backup.
Sintim was placed on injured reserve, meaning his roster spot will open up, and that could mean an opportunity for one of the team's rookie linebackers trying to make the squad. Greg Jones, Spencer Paysinger, Mark Herzlich, Jacquian Williams and Adrian Tracy are all fighting for roster spots.
Along with placing Sintim on IR, the Giants cut cornerback Darnell Burks, wide receiver Todd Watkins, offensive lineman Brant Clouser and defensive tackle Ibrahim Abdulai to get down to 80 players. They will have to cut down to 53 by Saturday.
Tuesday was the deadline for most NFL teams to downsize their rosters to 80 players. The Giants and New York Jets were given three-day extensions by the NFL because they played Monday night, 48 hours later than scheduled because of Hurricane Irene.
Sintim joins cornerbacks Terrell Thomas (ACL), Bruce Johnson (Achilles) and Brian Witherspoon (ACL), and second-round pick defensive tackle Marvin Austin (pectoral) as Giants who have already been lost with season-ending injuries.
Witherspoon said he's likely to have surgery on Tuesday. He said he expects to be back for the start of training camp next season.
Defensive end Osi Umenyiora, who is currently rehabbing after undergoing knee surgery a couple of weeks ago, still seems like a possibility to play in the Giants' regular-season opener at Washington next Sunday, according to Coughlin.
"We will see," Coughlin said. "Every day he looks better and better."
Coughlin said Umenyiora is currently working out at the team's rehab center.
First-round pick cornerback Prince Amukamara is out until perhaps the end of the month or longer with a broken foot.
Kiwanuka, who is currently nursing a groin injury, said he's "fine" and will be ready for the Washington game.
Kicker Lawrence Tynes, who hasn't played since bruising his right thigh in the Giants' preseason opener in Carolina, kicked 25 field goals and eight kickoffs on Friday, the third time he's kicked in the past three weeks.
"I feel pretty good, but I'm a little sore," Tynes said. "I haven't done anything in three weeks, but I feel like I'm ready. Coach will make that decision (if I play on Sunday), but I feel like I kicked pretty well. I'm just gonna continue through the weekend once more, and then I'll take off until Wednesday."
Tynes said he "definitely plans" on playing next Sunday in Washington.
He also kicked field goals in practice on Tuesday and Wednesday.
"It is an ankle injury (with Beckum) and if he would have played last night and reinjured it, it would have put him in jeopardy for next week," Coughlin said. "Same thing with Danny Ware, his back, and if something happened and he couldn't work Monday, it would not have been a smart move."
Mike Mazzeo is a frequent contributor to ESPNNewYork.com.