HITC Sport understands the Swede will arrive this week.
The 21-year-old is on the fringes of the first-team at the Estadio Da Luz with three appearances under his belt, but he is highly regarded at the club.
Boro, though, have now agreed a loan deal for the rest of the season with a view to a permanent deal, and they hope to have him signed before their weekend clash at Bristol City.
Middlesbrough boss Aitor Karanka and his staff have been scouring England and Europe for a player who can play in defence and midfield, as he wanted to cover the departures of loanees Jack Stephens and Bruno Zuculini who returned to their parent clubs, Southampton and Manchester City respectively.
Karanka admitted he would ideally sign just one player who could cover both areas, and Lindelof fits the bill as he can play in a holding midfield role, but is more of a centre-half.
Lindelof is now due in England to finalise the deal, and he is set to become Boro's second loan signing this week as Athletic Bibao forward Enrique Sola is also due to seal his switch to The Riverside in the coming days.
With his squad now seemingly covered in all aspects, Karanka will turn his attention to another top-line striker although their pursuit of Ross McCormack could be scuppered due to Fulham's transfer embargo and injuries to other players - but HITC Sport understands that he has other options and the club are prepared to pay big if the right player comes up.