The 20 year-old Swede is currently playing on-loan with IFK Norrkoping.
Fotbollskanalen reports Arsenal, United, AC MilanBenfica and Parma all had scouts in attendance in the Algarve to see Norrkoping's friendly against Brondby. And the subject of their interest was Haksabanovic and 18 year-old Brondby prospect Anis Slimane.
Indeed, Brondby defender Simon Hedlund confirmed: "No (they weren't here for me), I'm almost 27 years old, so it was probably some younger players that the clubs were watching, either Slimane in our team or Haksabanovic.
"Both were very good today."