The Red Devils are expected to cut veteran defender Patrice Evra loose at the end of the season, and have been heavily linked with a move for the Toffees ace to replace the Frenchman.
However, failed bids over the summer for Baines have raised concerns that the England international may be out of their reach, with the Merseyside club reluctant to sell, arguably, their most influential player.
As a result, Moyes is shopping around for alternatives, and has been impressed by Sandro.
The 22-year-old has been one of the Portuguese giants’ standout performers in recent times, and caught the eye of the Old Trafford boss during a recent scouting mission to watch a tie between his side and Atletico Madrid.
Porto are thought to value their defender at around £8m, and are a club known for selling their talented stars to larger European clubs.
The Brazilian ace has made six appearances for his national side, and could be in with a chance of making their squad ahead of the World Cup.