The 19-year old Brazilian right-back signed with the Blues in January but did not arrive at Stamford Bridge until this summer after remaining on loan with former club Fluminense.
Despite impressing in pre-season, Wallace will again be sent away for further first team development as Mourinho looks to him for the future.
"He's a very good player - but he won't be staying with us because we have (Branislav) Ivanovic and (Cesar) Azpilicueta for the same position," said Mourinho.
"Because he is non-EU we'll not get the work permit, it'll be too early, so he'll go on loan for a season.
"We'll get the best option for him, in Europe. We want him to adapt.
"He's very mature for his age, comfortable with the ball. He has the quality of a Brazilian full-back, likes to attack and create.
"So we'll see the best of him: he has talent and is one more investment for this club, a good investment, because the kid is a very good player."