The injuries are starting to mount on the New York Giants' offensive line.
The Giants will find out how long Seubert will be out when he is examined by Dr. Russell Warren on Saturday.
Seubert was the second offensive lineman to go down, joining two-time Pro Bowl center Shaun O'Hara, who has been sidelined since Monday with swelling in his left ankle.
Free agent lineman Reuben Riley also suffered an injury to his medial collateral ligament in his left knee on the last play of practice on Friday, Coughlin said. There is no immediate word on how long he will be out.
The Giants open their exhibition season on Aug. 16 against the Jets in the first football game at the New Meadowlands Stadium.
Coughlin said O'Hara is due back Monday, along with safety Kenny Phillips, who missed most of last season with a major knee injury.
The coach said that it's a fallacy to think an offensive lineman can simply tape his hand, put a cast on it and play.
"If the metacarpal twists, they have to do surgery, put a pin it in and it's out for six weeks," Coughlin said after practice ended Friday.
The coach said if the broken bone is given a little time to heal, it's more likely the player will be back sooner.
"We're not going to let him go right back out," said Coughlin, who saw his team battle injuries last season in missing the playoffs with an 8-8 record.
Fifth-year lineman Guy Whimper worked with the first team at guard on Friday while Adam Koets continued to fill in for O'Hara.
Seubert was hurt on Thursday night while blocking during a passing play in the team's first full pads workout. He was on the field for the next play before coming off.
The 31-year-old wore a splint on his left wrist and arm when he arrived at lunch on Friday. He deferred questions to Coughlin.
Seubert came to training camp knowing that the Giants were considering some changes on the line after it struggled opening holes for the run last season. The rumor was that left tackle David Diehl would be moved to Seubert's spot and second-year pro Will Beatty would start at left tackle.
Coincidentally, Beatty had a horrible practice on Thursday night and had offensive line coach Pat Flaherty scream at him, telling him to "Wake Up."