In the modern day world of football, making a right signing and a wrong signing can potentially cost a managers job. Managers are under great pressure these days to buy the best players, for the lowest prices, although you wouldn't think it by looking at the January transfers.
Being a "proven" player is usually quite important for potential buyers. Spending a considerable amount of money on a player from a foreign country, for him to come into the Premier League and crumble isn't going to be the deal of the century. How long does a player have to play in the Premier League for him to be considered "proven"?
I would argue nowhere under 3 years, minimum.
In July 2007 Roque Santa Cruz was bought by Blackburn Rovers for a fee around 3.5m In his first season he scored an impressive 19 league goals placing him as the 4th top scorer in the season and was hailed as an incredible buy. However it was not meant to be.
The following season Santa Cruz netted a measly 4 league goals and despite this apparent minor blip, enter Manchester City, who are never shy to flash their cash. Santa Cruz moved on June 2009 to City for £17.5 million. He has scored 3 league goals since.
Unfortunately for him, it can be argued Roque Santa Cruz is unproven and can be considered a "one hit wonder" unless he can rekindle the sensational form he had in the first season, now back on loan at Blackburn.
This is the kind of risk the modern day manager has to take, if it comes off, you will be hailed a genius. However should it fail, the results can be disastrous.