The healthcare company could be valued at more than £100m, said Dow Jones, citing two people familiar with the matter.
Sovereign has been following a dual-track sale process, considering both an IPO and an outright sale.
Graphite, which is headquartered in London, recently made a return of 2.3 times from the sale of UK caravan park operator Park Holidays UK for £172m and a 3.5 times return from its exit from Alexander Mann Solutions, which was sold for £260m.
In September this year Graphite closed its eighth fund on £475m and said that it expected to secure more commitments to bring the fundraising total to more than £500m.
The fund, which is the largest vehicle dedicated to investing in UK companies raised in the past five years, will target businesses with an enterprise value of £40m to £150m. It will also back smaller companies with the potential to expand through the roll-out of new sites.
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