Heitinga, 27, said: "I can honestly say I feel annoyed at having the day off when I'm on the couch watching Champions League football on Tuesdays or Wednesdays.
"It's the same on Thursdays with the Europa League. European football is a big miss for me.
"Everton is a genuine big people's club. The atmosphere at Goodison is unrivalled, and I'm playing in a fantastic league.
"But I am ruling nothing out this summer. I have three years left on my contract and could see it through - but a new possibility could come up.
"In that case I will think about leaving."