The case involving the pair has to date centred around a CHF2 million (£1.6million/$2.2million/€1.8million) payment made by Blatter to Platini in 2011.

A criminal proceeding has been open against Blatter, 84, since the allegation was revealed in September 2015, and was extended to Platini in June.

Both maintained the payment was made as part of an oral agreement for work Platini carried out for Blatter between 1998 and 2002, but FIFA's Ethics Committee dismissed that claim and its ruling was later upheld by the Court of Arbitration for Sport.

Switzerland's Blatter, who was FIFA President for 17 years before leaving the post in June 2015, was banned from all football-related activities for six years.

Platini received a four-year ban over the affair.

According to French newspaper Le Monde, Blatter and Platini have been informed by the Swiss Office of the Attorney General that the case has been widened, having "adopted a different point of view from that which it had previously on an aspect of the procedure" regarding the payment.

It is claimed that Blatter is under investigation on "suspicion of fraud, breach of trust and unfair management", while Platini reportedly is under suspicion of "forgery in securities and participation in unfair management", as well as "fraud and possible breach of trust".

Blatter had been questioned at the Office of the Attorney General in Bern back in September.

Platini, a former French national team captain, had attended questioning a day earlier.

Both Blatter and Platini have denied wrongdoing.

"I have a good conscience and have nothing to reproach myself with," Blatter told Le Monde.

Representatives of Platini said: "This judicial harassment has lasted too long.

"We will challenge with the greatest vigour and by all means these new accusations which are pure judicial conjecture.

"Michel Platini has been since 2015, i.e. five long years: witness, assisted witness, then officially cleared by the same MPC (Public Prosecutor's Office) in 2018, then suspect interviewed on the basis of suspicions raised by the last hearings.

"The MPC is now seeking to reclassify these same facts in an attempt to artificially justify the continuation of this interminable procedure.

"It is truly astounding for the justice of a country like Switzerland."

Platini’s four-year ban from football ended in October.