The Dutch striker's £24million move to Manchester United is expected to be completed soon after he passed a medical and Vermaelen is well aware just how good he was in scoring 30 Premier League goals last season.
But the Belgian defender says it would be careless of the Gunners to worry about not having van Persie present as he focuses on the upcoming campaign which kicks off against Sunderland on Saturday.
"He was fantastic for us in the last year, scored lots of goals and I am disappointed he is going, but we have to focus on the next season with Arsenal," Vermaelen told Sky Sports News.
"We have to fight and I am confident we have a squad to win something.
"We start Saturday and this is all clear now, Robin is leaving and we have to move on."