Wenger would have preferred to sell Van Persie to PSG
Van Persie is expected to complete his move to Old Trafford within the next 24 hours after Arsenal accepted a bid of around £22 million ($34 million) for their captain.
To have sold the Dutch international to a rival team was "a negative point, which we wanted to avoid at any price, but we could not", Wenger said in a video released by French broadcaster TF1, for whom he does football commentary.
"Honestly, I would have preferred to have sold him overseas, to PSG for example, rather than Manchester United.
"He's an exceptional player in the pure sense of the term. I haven't seen many in my life who have that quality in the first touch, are so technically gifted and have that intelligence of movement in the final 20 metres.
"Unfortunately, there's an economic reality and the desire of the player. There's no other way but to leave him go.
"It's another pill to swallow, we've swallowed other ones and we've always survived, but he scored 30 goals for us in the league last season, practically one every match."
The Holland international scored 37 goals for Arsenal in all competitions last season and his departure is a significant blow to their hopes of ending a seven-year trophy drought.
"The economic factor is the sole satisfying thing, but you don't play with money on the pitch, you play with the quality of the players. To lose a player of this ilk is tough," Wenger said.
"It will give more chances to (new recruit Olivier) Giroud because when Van Persie is there, he's hands-down the first name on the teamsheet, and then you pick the others around him. There's a gap to fill, it's up to whoever wants to seize their chance."
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