The Swiss official is perplexed as to why the Nerazzurri are taking so long to finalise the deal to sign the centre-back
Both parties are believed to have thrashed out an €8 million (£6.9m) deal in principle for the 22-year-old, but the Nerazzurri are yet to finalise proceedings.
And, speaking to Basler Zeitung, Heitz believes the switch may have been completed by now if the Swiss club were of a larger stature within the game.
He said: "We have reached an agreement with Inter, now we just wait for them to finalise the deal.
"We have been waiting for days to complete the deal and we do not understand why they are behaving this way. Maybe because Basel is a small club?"
The Austria international, whose deal at St. Jakob Park runs until 2015, has made 66 appearances for the club throughout his three-year stay in Switzerland.