Analysts at Charles Stanley Direct have removed the £19.2bn Fundsmith Equity fund from the provider's favourite fund list.
The Fundsmith Equity fund is run by Terry Smith, and is the absolute top performer from 205 funds in the IA Global sector over the past five years, returning 179 per cent in that time compared with 67 per cent for the average fund in the sector.
Rob Morgan, fund analyst at the Charles Stanley Direct platform, said the size of the fund meant it might struggle to replicate that level of performance in the years ahead.
In a statement on the firm's website Mr Morgan wrote: "To us, a developing issue is the size of the fund, which we believe may, at some point, become more of a challenge for the manager.
"At around £19bn it is the largest UK retail fund and it continues to attract substantial inflows from investors.
"As a fund grows in size it can sometimes mean the loss of flexibility in terms of the number of available investments."
Mr Morgan acknowledged that the "counter-argument" was that Fundsmith’s strategy was focused entirely on large and mega-sized companies which made it more scalable than other funds.
He wrote: "Holdings are generally exceptionally liquid, meaning they are easy to trade in large quantities.
"Unlike many active managers who have to contend with rapid asset growth Mr Smith isn’t constrained by an inability to invest in small and mid-cap firms – the fund hasn’t ever invested in these parts of the market.
"In addition, Mr Smith operates a ‘buy and hold’ philosophy, which means he only rarely trades in and out of holdings."
He added: "Yet the fact remains that the fund continues to forge into unchartered territory in terms of its size, and this presents a small discomfort to us on a longer term view."
Charles Stanley Direct is a direct to consumer investment platform, which reviews its buylist every month.
Darius McDermott, managing director at Chelsea Financial Services, said: "There is no doubt that Terry Smith and Fundsmith had done a great job for investors, it is just under £5 a unit now, and when the fund launched it was £1 a unit, and it is the best performing fund in its sector since launch.
"It is definitely relevant to ask about the size. But the key is that it is invested in very large holdings, and they have assured us that if there was a very big redemption they could deal with it."
A representative of Fundsmith declined to comment.