Tomorrow afternoon we will know the make-up of the Champions League semi-finals. After overcoming Barcelona, Atletico Madrid will be hoping to avoid Chelsea in the last four, and indeed the final should they make it.

Why? It’s not because they fear Jose Mourinho’s side, but rather because their first choice goalkeeper Thibaut Courtois is on loan from the London side since 2011, and were Atletico to field him against his parent club, it would cost them in the region of €3m.

While there is no denying the short-term benefits of loan arrivals to smaller clubs, the system is weighted in favour of clubs like Chelsea. Clubs who can afford to buy high quality players then send them on loan to gain experience instead of parachuting them immediately into the first team. These high quality players in many cases end up playing in the same league as their parent club, yet clauses in the loan deal stipulate that they cannot compete against them.

A case in point is Romelu Lukaku. The Belgian striker joined Chelsea for around £17m (including add-ons) in 2011. After a relatively underwhelming debut season, the 20 year old has matured into an exceptional attacking threat. Not for Chelsea, however. He joined West Bromwich Albion on loan in the summer of 2012 and went on to score 17 goals in the league for his adopted club. That was more than any individual playing for Chelsea managed that season. He scored for the Baggies against Liverpool, and netted a hat-trick against Manchester United on the last day of the season before returning to Chelsea for the summer.

On transfer deadline day last September, despite featuring in two of Chelsea’s early league games, Lukaku moved to Everton on loan after being deemed surplus to the requirements of Jose Mourinho. This season he has again been in good scoring form, with 13 so far. He (along with other loanees Barry and Delofeu) has been a vital component of Everton’s pursuit of Champions League football, and of Chelsea’s title tilt. His two goals in the first Merseyside Derby of the season prevented Liverpool from taking all three points. He scored last weekend against Arsenal to once and for all dump them out of the race for the Premier League trophy.

It didn’t go unnoticed by other managers in the league that Mourinho may have loaned out Lukaku primarily to take points off of Chelsea’s direct rivals. The fact that he couldn’t play against his parent club may also have shaped the title-race. In a tight game at Stamford Bridge in February, Chelsea took three points with a late John Terry goal.

The Blues aren’t the only team who have used the loan system to their advantage however. When Sunderland beat Chelsea 3-0 in November 2010, on loan Manchester United striker Danny Welbeck put in a man of the match performance, scoring one in the process.

It might be naive to hope for a system where on-loan players can line-out against their parent club, particularly in the same league. But when it obstructs a young player’s opportunity to play in the biggest games, such as it could with Courtois, then the system is inherently flawed.

After three years as Atletico’s number one, the Belgian will decide on his future at the end of the current campaign. Chelsea view him as a long term successor to Petr Cech, and he may return to Stamford Bridge in the summer to challenge the Czech keeper next season. But were he to miss out on either a Champions League semi-final or final because his presence in goal would disadvantage his parent club, the only parties that would benefit would be Chelsea and Daniel Aranzubia, Atletico’s number two.