Sports Direct International looks odds on to join the FTSE 100 at next week's reshuffle, along with recently listed Coca-Cola Hellenic.
Mike Ashley's retailing group - which was recently found to employ 90% of its staff on so-called zero hour contracts - has seen its share price jump more than 70% this year as it boosts profits and takes market share from struggling rivals.
Meanwhile Greek bottling group Coca Cola Hellenic, which listed its shares in London earlier this year, is now eligible to join the UK indices and is large enough to move straight into the FTSE 100.
Another outside entrant for the leading index is South African paper maker Mondi.
Relegated to the FTSE 250 to make way for the newcomers could be Serco, Eurasian Natural Resources Corporation and - if Mondi joins - Wood Group.
According to analysts at Edison, companies which could be promoted to the FTSE 250 are Partnership Assurance, Al Noor Hospitals, Cineworld, Greencore Group and Entertainment One.
This would be at the expense of Schroder Asia Pacific Fund, Utilico Emerging Markets, JP Morgan's Indian Investment Trust, Anite and Salamander Energy. Edison analyst Gareth Jones said:
The net impact of the changes will be to slightly tilt the bias of the index towards domestic/developed markets and away from (Eastern) emerging markets.
