It has been reported that the ex-Gers chief is weighing up a bid for the 26-year-old, who he brought to Ibrox from Swindon Town in 2015.
Foderingham and Bournemouth's Adam Federici are the two goalkeepers being linked with moves to the City Ground amid claims that the Forest boss is chasing a new number one.
Warburton confirmed he is closing in on a new signing, but refused to reveal whether Foderingham was on his shopping list.
He said: "We are very close with one and there may be one more after that. We will see.
"[Foderingham] is one of only 49 players we have been linked with this summer, isn't he?
"But we signed him at Rangers and I have a lot of respect for him, which started before that, from his time at Swindon.
"He is a Rangers player. I have enormous respect for him, because he is a tremendous keeper.
"But he is a Rangers player and I do not like to talk about players who are at another club."