Vista Equity Partners has reportedly made a £1.2 billion bid for Misys.
The move comes during ongoing merger talks between the UK financial software giant and Swiss software firm Temenos.
The offer, reported by the Financial Times, could appear attractive to some shareholders after they questioned how long it will take to achieve savings in a Temenos merger. Vista also recently bought Kondor, the trading and risk management business of Thomson Reuters that Misys itself had been looking at buying, the FT noted.
Neither Misys nor Vista has commented on the value of a potential offer.
Misys said in a statement today that it "confirms that it has received an approach from Vista Equity Partners, consisting of a non-binding indicative proposal to acquire the entire outstanding share capital of Misys for cash". The move "may or may not lead to an offer being made", it said.
Other private equity companies are said to also be considering making an offer.
The existing Misys-Temenos talks have attracted some speculation about the prospects of UK jobs, after Swiss-based Temenos said the headquarters of the combined firm will be located in Switzerland and headed by its current CEO.
UK headquartered Misys employs a global workforce of 4,000 and has been looking for a potential buyer for some time. Last year there was an aborted takeover by US firm Fidelity National Information Services (FIS), after Misys said the bid undervalued the company following a year when profits rose by 12 percent.