Moyes said: "He has done really well in Belgium, we have been watching him for a while and a lot of people said it was a last-minute deadline [purchase] but we have known about him for a long time.
"What probably put him over the edge was his performances against Liverpool - that tipped the balance and I thought 'maybe this is the time to try and get him'.
"When you play against Liverpool you are playing against certainly one of the best teams in the Premier League and one of the best in Europe. It made us realise that the potential we saw in him in Belgium had now come to [fruition] and that he was now ready to come play in England. I managed to watch Standard in their following game as well and again he had a big impact and affected the game as he did against Liverpool which backed up our feelings about him and the reports from the scouts.
"Hopefully all is best days are still to come."