According to reports, Manchester United had a scout in the stands as FC Porto defeated Arsenal in the Champions League last-16 first-leg on Wednesday night. Now, Portuguese publication Record does not go any further than that, providing no further information about the reason for the Red Devils’ trip to the Estadio do Dragao. But there is one name on the Porto team-sheet that will be familiar to Manchester United supporters. Diogo Costa, after all, spent much of last year being linked with a to Old Trafford before Erik ten Hag opted to reunite with Andre Onana instead. And his stellar display …