Bolton No.2 keeper Ben Amos was linked with Cardiff City.
The former Man Utd keeper is still under a long contract at Bolton but is not first choice this season.
Cardiff sold Simon Moore to Sheff Utd last week with Ben Wilson on the bench for City at Fulham. But Amos could become Marshall's understudy if he were to sign.
City have also been linked with another Man Utd keeper. This time Sam Johnstone.
When asked today about the link with Amos, Paul Trollope said:
"At this moment I am not going to talk about individual players.
"It is well documented we are looking at areas to strengthen before the window closes.
"Once anything is done we can have a good talk about it but for the moment I am not going to talk about individual players.
"Needless to say there are two or three positions we are looking for and we are working hard to secure what we want."
Another player linked is Norwich City striker Kyle Lafferty. The Northern Ireland striker scored seven goals as Northern Ireland qualified for Euro 2016 but he's no more than a finge player at Carrow Rd with only three goals in two years.
It's unknown how serious City's interest is.