Villa remain in talks with Southampton over Taylor Harwood-Bellis after seeing a second bid for the defender rejected.
Discussions are also continuing with Club Brugge concerning Joel Ordonez, with both centre-backs being considered as replacements for Ezri Konsa following his move to Arsenal last week.
Reports in Belgium on Monday claimed Villa have agreed personal terms with Ordonez, though the two clubs are thought to be some way apart on value.
The move is complicated by the fact the 22-year-old Ecuador international is sidelined with a foot injury.
Harwood-Bellis was left out of Southampton’s win over Stoke at the weekend due to doubts over his future.
Villa’s latest bid was an improvement on their first offer of an initial £18million but was still not enough to satisfy the Saints.
Recruiting a centre-back is a key focus over the final week of the window for boss Unai Emery, who watched his team concede four times in 23 minutes during Sunday’s season-opening defeat at Brighton.
Villa are also preparing to move on forward targets should there be a resolution to the situation surrounding Ollie Watkins.
The England international wants to join Al-Hilal but an agreement between the clubs is not currently thought to be close.
Chelsea’s Nicolas Jackson is a long-time target, while Villa are among the clubs keeping an eye on Jean-Philippe Mateta’s situation at Crystal Palace.
Former Bayern Munich midfielder Leon Goretzka is expected to join later this week on a free transfer to bolster Emery’s options in the middle of the park.
Aston Villa in talks over two defenders after bid rejected