According to CBS Sports' Jason La Canfora, the Lions are shopping for a quality safety they would be able to use in the starting lineup if current starter Louis Delmas were to miss time.
Delmas, who had knee surgery during training camp, missed the team's first four games and injured the same knee when colliding with a teammate during the Lions victory against the Seattle Seahawks on Sunday.
The Lions classified Delmas as day-to-day on Monday.
"Well, he had some tests today," said head coach Jim Schwartz. "You know, he's day to day, he's sore. I don't know if I can classify it as a re-injury, but it's his sore knee that's been bothering him through training camp and the season. You know, he's a hard worker, tough guy. We'll try to work through it."
It's also possible the team is concerned about safety Amari Spievey, who missed the team's last game with a concussion.
"It's a little too early to tell with Spievey," said Schwartz. "He's still got some hurdles to clear. But both of those guys (Spievey and cornerback Jacob Lacey) are doing well and they're on their way back. It's just how long that will be and whether or not it will be this week. We'll get a better feel for it later in the week."
The Lions obviously won't comment on any deals before they occur but it is clear they are willing to talk about potential deals with teams.
"There's not a day that goes by that we don't think about a different way to improve our team," said Schwartz. "I think that Martin (Mayhew) has been very strong in what he said consistently over time is that there is no finish line when it comes to personnel. Any path that we can take to improve our team we are certainly willing to look at."
Mayhew has demonstrated a willingness to make deadline deals, striking three in his five seasons as general manager.
In his first season, when he took over for Matt Millen, he traded under performing receiver Roy Williams for a first-round pick. Last year, he traded running back Jerome Harrison for running back Ronnie Brown but the deal was voided when Harrison failed his physical and this year he has already dealt for Jacksonville's Thomas.