Dean Smith was eager to offer Trippier a route back to the Premier League after a season in Spain with Atletico Madrid.
But talks over a deal for the England international have not progressed as Villa had hoped in recent days and attention has now turned to the highly-rated Cash.
Villa are thought to have had an initial offer of around £10million rejected by Forest, who are holding out for a fee of £15m.
The 23-year-old enjoyed an excellent season in the Championship and has no shortage of top flight suitors, with newly-promoted Fulham expected to make a move in the coming days.
Villa boss Smith has identified the right-back area as an area which requires strengthening during the current transfer window.
Ollie Watkins remains his primary attacking target and Villa are hopeful of a breakthrough in talks with Brentford over the coming week.
Watkins, who was this week named Championship player of the season, can also play out wide and Smith wants to sign a more traditional centre-forward in addition with record buy Wesley not expected to return from injury until later in the year. Keinan Davis may be allowed to leave on loan.
A new midfielder and goalkeeper are also among Villa’s priorities in the window.