The phrase "a sizeable fan" is correct and usable in written English.
It can be used to describe a significant or large number of fans or supporters of a person, group, or thing.
Example: "The band has a sizeable fan base that attends their concerts regularly."
Alternatives: "a substantial fan" or "a large following".
By the time the record labels came calling in 2011, he was already selling out shows and had a sizeable fan base due to an astute use of social media.
And so when Morales came along, he was seen as a breakthrough by many - an A-list non-white character with critically acclaimed stories and a sizeable fan base.
Despite his misdemeanours, he retains a sizeable fan base.
Program them to deliver burgers and lotto tickets, and I have a feeling they'll gain a sizeable fan club.
She says that because she's in a position of power ― a top-tier dancer at a top-tier company, with a sizeable fan base and following.
Up to this point, drum and bass had amassed a sizeable fan base but still remained outside the realm of mainstream electronica.
For a sizeable fee, fans can spend all of eternity (well not quite eternity, €6,000 gets you 90 years) in the Barcelona mausoleum.
There are those, possibly even among Leicester's sizeable fan base, who will have doubts as to whether the same scenario will be played out at the Walkers Stadium, where Eriksson will take charge for the first time tomorrow against a Hull City side under the stewardship of Nigel Pearson, who led the Foxes to promotion 18 months ago.
The teams from the North East have sizeable fan bases, but the region is relatively poor, and at national level they are rarely serious challengers.
A sizeable contingent of fans gather around them, some wearing retro National Soccer League jerseys and jackets, others wearing Croatian national shirts.
As the Call of Duty series has moved further and further into the future, a sizeable number of fans have yearned for a return to historic or at least contemporary settings.
