Rooney signed a new deal on Friday, thought to be worth around £300,000-per-week, and the former Reds boss has said that while he feels the deal is a good move for United, it will mean that potential new signings will be asking for similar wages.
He told The Mirror: "Signing Wayne is great news for United, but it also gives them a problem with new players coming in, looking for a deal that's on a par with what he's getting.
"So in that respect it could prove a bit awkward for United. They're a financially sound club with a huge turnover, but they may find the agents of players they want to sign this summer using Wayne's new wages as a barometer of what they want.
"It doesn't matter about their ability, they'll just look at Wayne's wages. These players might not be a patch on Wayne in terms of ability, but that won't stop them looking for money they're not entitled to."
Rooney's deal makes him the highest paid player in Premier League history.