Foster has impressed on-loan from Birmingham City this season.
Downing said: "I think there's a respect for Birmingham. They're obviously licking their wounds after the play-off defeat.
"Ben has played exceptionally well and he's got better and better as the season has gone on.
"We would be stupid to turn that sort of interest (in signing Foster) away but I'm sure other clubs as well will be interested. We are trying to pursue that."