It has been reported that the Blades have made a bid of £10 million for Cash, but Championship club Forest have turned it down.
The report has claimed that the Hammers and the Saints are also set to make bids for the right-back, with the London club have had a £12 million offer turned down by the Reds for the 22-year-old right-back.
It has been added that Forest will accept offers of up to £15 million after instalments for the youngster, who can also play as a midfielder.
According to WhoScored, Cash made 40 starts and two substitute appearances in the Championship for Forest this past season, scoring three goals and providing five assists in the process.
The 22-year-old made 27 starts and nine substitute appearances in the league for the Reds during the 2018-19 campaign, scoring six goals and providing one assist in the process, according to WhoScored.
Forest narrowly missed out on the Championship playoffs this past season, and will be looking to launch a challenge for the top-six in 2020-21, and for that they need to keep hold of their best players.