Arsenal won against Leicester 2-1 at the Emirates Stadium in North London on February 14.
Vermaelen, who played for the Gunners from 2009 to 2014 before leaving for Barcelona, watched the game.
The 30-year-old Belgium international centre-back has revealed that he felt stressed while watching the match, which ended in a 2-1 win for Arsene Wenger’s side.
The former Ajax star has also commented on Arsenal’s chances of winning the Premier League title this season.
“I watch a lot of Arsenal games because I have warm memories of the club, and because they are a very attractive team,” Vermaelen told The Telegraph. “I watched the Leicester game last week, it was very stressful but these are the most beautiful games to win.
“Now the title race is wide open, if they hadn’t won it would have been more difficult but now it’s on. I always said at the start that Arsenal had a big chance to win it. Unfortunately we had to go our separate ways but luckily I signed for a beautiful club like Barcelona.”
Arsenal will return to action on Tuesday evening when they take on Barcelona in the first leg of the Champions League last 16 at the Emirates Stadium in North London.
Barcelona will head into the encounter as firm favourites, but the Gunners can force a draw and keep the tie alive for the second leg.