The private equity firms confirmed Hellman & Friedman's participation in a statement but added that a deal has not yet been made.
"There can be no certainty that an offer will be made, nor the terms of which any offer would be made," the statement read.
Providence and Carlyle admitted last week that they had approached the publisher of Lloyd's List with a cash offer, but did not disclose how much the offer valued the company at.
The bid is expected to be 450p-550p per share. A 500p per-share deal would value the company at more than £2.1bn.
In early morning trading, Informa shares were sitting at 430.75p, up 1.06% on Friday's close.
Early last week, Informa and rival business media company UBM called off talks about an all-share merger.
UBM had made the approach but found itself priced out of a deal when interest from private equity in Informa propelled its share price upwards.
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