Around £16.6m of shares, which are thought to be equal to 10% of the club, were put up for public trading for the first time in seven years, with shares being sold for £9.
"They own the club. They are entitled to sell to investors who want to be a part of Manchester United going forward," said Gill.
"What I would say is that the level of debt in the club since they have taken over hasn't had an impact on what we have done in the team.
"We fully understand, and the owners fully understand, that what happens on the pitch is crucial and we will make sure that we have sufficient funds to invest in the team going forward."
Reports have claimed that the American family are expected to receive £75m.