Stafford said he believed he had his hand stepped on after throwing an interception in the fourth quarter. He was almost immediately taken to the locker room and did not return for the Lions' final nine offensive snaps.
"It was a pretty nasty bruise, but it looked normal," Caldwell said. "No break in there at this point."
Stafford had his right hand heavily bandaged after Sunday's loss when he spoke to the media and said "it happens" about his hand getting stepped on.
He said he didn't know whether his hand was broken at first and that he "couldn't really feel it too well, to tell you the truth," adding that he had "some burning nerve pain in there, so I didn't know what it was going to be, but X-rays were negative."
The injury came after Stafford threw 20 straight completions, a team record. He completed 24 of 29 passes for 292 yards with one touchdown and one interception while being sacked three times.
Stafford missed his first snaps since Week 8 of the 2015 season against the Kansas City Chiefs in London, where the Lions were blown out 45-10.