The 18-year-old was called up by coach Carlo Ancelotti after injuries to Lucas Vazquez and Dani Carvajal, but Ancelotti chose to use Nacho Fernandez instead in recent games against Villarreal and Athletic Club.
Tobias, who is highly-rated, joined Real Madrid on loan from Shakhtar Donetsk until the end of the 2022-23 season, with an option to buy for 18 million Euros.
However, Shakhtar Donetsk chief Sergei Palkin has recently stated to Marca that the player could return to Ukraine at the end of the loan period.
"We contacted Madrid a month ago and informed them that if they didn't need him, we would have him back.
"They told me that they want him until the end of the season and we will make a decision at the end of the season. We get along well with Madrid," Palkin said.
Tobias has yet to make his first-team debut for Real Madrid, but has been a regular at Real Madrid Castilla under Raul Gonzalez. He has started 90% of their games, providing four assists.
It is understandable that Real Madrid are still uncertain about committing a large sum of money to a player who has yet to make a senior appearance in European football.