He knows it could happen to Miami Dolphins quarterback Dan Marino -- it happened to Kosar often enough in those nine years he was the stoutest thing in Cleveland -- but Kosar prays Marino "never takes a shot like that."
Football's most famous backup quarterback concedes there's a part of him "that misses playing." Just as quickly, he adds, "But no way do I want to get in there because something happens to one of my best friends."
They have grown tight, the 33-year-old Marino with his 315 touchdown passes, and the star sub who people forget threw for 119 TDs in Cleveland and Dallas. Although this is his 10th pro season, Kosar won't even be 31 until next week.
"This is Dan's team, Dan's offense," Kosar says. "Sure I'd like to play, especially when -- and don't take this the wrong way -- you look around the league and see how some of the QBs are struggling. But I knew the situation when I came here. Dan is the man."
Kosar doesn't have to say he could be starting in much of the NFL, probably with the New York Jets, the Colts, Oilers, Bengals, Giants, Redskins, Cardinals, Bucs, Rams, maybe half of the league's teams.
In fact, it has been so long since Kosar was healthy and not playing, he can barely remember when he was an 18-year-old freshman at Miami.
The next season, 1983, he stepped in and steered the Hurricanes to their first national championship. After that he was always The Man until last season when Browns coach Bill Belichick cut him in one of the great gaffes of NFL coaching.
Kosar wears a Super Bowl ring from the Cowboys. He hasn't played the first play for the Dolphins, but he runs the killer gassers just as though he would be running the team each Sunday.
Sometimes it takes a big man to take a smaller part. Kosar did it for the same reason he has always done everything, for his family. I remember him as a Hurricane talking endlessly about mother, father, brother and sister back in Boardman, Ohio.
He still talks about them, but he has more to talk about now -- wife Babette and daughters Sara, 3, and Rachel, 2. They are the reasons he is a Dolphin.
"We lived in about four different houses in that 10 months when I was with the Browns and then the Cowboys." Back home in Weston Hills, he "can see the difference in the girls' growth and learning."
That kind of thing was, is, what makes Kosar tick. He was an honor student at UM. Now he finances two scholarships at UM, and more at Cleveland State and Youngstown State -- and puts in every Dolphins workday just as though he would be starting and playing all day Sunday against the Patriots.
So how hard it is to sit every Sunday?
"I'm not going to kid you, it's hard." It is even harder because Kosar is as fierce a competitor as Marino. You have to know him to believe it when he says he wants to see "my friend do well," meaning Marino.
"That's why I have such great respect for him, for his talent, for his competitiveness. I knew exactly how it was going to be here, and I'm willing to have it that way to be at home and with a team that has a good shot at a Super Bowl."
They have another semi-family thing going there, old pros Kosar and Marino, plus Kosar's UM offensive coach, Gary Stevens, who runs the Dolphins' offense. In fact, Kosar took the trouble before the Miami-Florida State game to call Hurricanes quarterback Frank Costa and advise him not to let the carpers get him down. Back at Dolphins Central, he and Marino and Stevens all know what to say to each other, and what not to, and when Marino sometimes blows a gasket, they know about that, too.
"I can relate to that," says Kosar, who has been a steam-whistle himself; recall the moment late in UM's '84 classic with Boston College when Kosar screamed at UM coach Jimmy Johnson on the sidelines. Only Bernie could get by with that.
Kosar can relate so well he often says exactly nothing when Marino comes to the sideline.
"Sometimes," Kosar says, "the less said to a man the better. Sometimes you just need to be alone and cool off. Sometimes you don't need somebody chirping in your ear and giving you a long-winded answer."