Manchester United snapped up Robin van Persie two seasons ago, the former Arsenal captain going on to win his first Premier League title in the subsequent season. However Danny Welbeck has since traded places as well. He left United for Arsenal in a £16 million deal this summer.
Since moving from United to Arsenal Welbeck has looked an improved player. He may still not be scoring the goals on a regular basis in the Premier League, but his performances in the Champions League have been superb.
Manchester United's manager thinks he knows why.
Van Gaal believes that the fact Welbeck is playing in the same position week in week out is doing him wonders at Arsenal and is the reason for his apparent improvement.
"A player (Welbeck) who plays in a fixed position in a team develops better. So he takes all the benefit that he plays every week. That was a question mark with Manchester United. So it's very good to see him doing what I thought."
During his time at United Welbeck was often shifted around the front-line, never truly receiving a chance as an out-and-out striker.
At Arsenal he has instead been playing through the middle and it certainly appears to be suiting him better than never knowing whereabouts he will play week after week.
Van Gaal will hope that his decision not to give him that chance at Old Trafford will not come back to bite him on Saturday.