Fans are urged to buy in advance for this weekend's pre-season friendly against Real Betis.
National League side Chesterfield plays host as the Teessiders take on the La Liga outfit on Saturday 22 July (kick-off 2pm).
Real Betis, managed by Manuel Pellegrini, finished sixth in the Spanish top flight last season and will present a welcome challenge for Michael Carrick's side.
Over 5,000 Boro fans watched our opening UK friendlies at Hartlepool and York over the weekend.