The Sun says Blues coach Roberto di Matteo watched the 19-year-old play for his country against Germany in Stuttgart.
Chelsea have been on his trail since before Andre Villas-Boas took charge. They made an unsuccessful move in January, failing to match the release clause terms.
They were given permission to speak to him a few weeks ago, but Santos said they were no longer interested in selling him.
Now Di Matteo's report will determine Chelsea's next move.