Signing players on loan and then making the move permanent is always safer for clubs than making an outright big-money transfer. One can only imagine if Manchester United had forked out £43.5 million for Radamel Falcao instead of loaning him out.Clubs send young players on loan to gain valuable first-team experience. Underperforming and fringe players are loaned out so that they get a shot at rejuvenating their careers and accrue games under their belts.Clubs that don't have deep pockets can do wonders with the loan system. An on-loan player can be signed up permanently if he impresses on loan.A loan deal can prove to be an astute piece of business. Take Zlatan Ibrahimovic's loan move to AC Milan as an example. The former Inter Milan striker's switch from the Nerazzurri to Barcelona proved to be one of the biggest transfer follies in recent times. But his subsequent loan deal to Milan yielded 21 goals and a Scudetto in 2011.On that note, let's take a look at five on-loan players who could be signed permanently this summer.#1 Arkadiusz Milik (Napoli/ Marseille)Arkadiusz Milik after winning the Coppa Italia final with Napoli last season.Azkadiusz Milik joined Marseille on loan in January. The Polish forward has enjoyed a brief renaissance at the French club after being sidelined by Napoli.In 15 appearances under manager Jorge Sampaoli, Milik scored nine goals- overtaking the Mexico-bound Florian Thauvin and star forward Dimitri Payet. The 27-year old also fired a hat-trick against Angers SCO to secure European football for Marseille next season.As soon as I arrived here I immediately understood how important this club and this shirt was. The Europe League qualification is a good goal, I always tried to give my best. I want to thank my teammates, clubs and above all the fans who made me feel at home. Allez OM pic.twitter.com/bM5c5pcDUg— Arkadiusz Milik (@arekmilik9) May 24, 2021The Arkadiusz Milik transfer saga seems like a never-ending one, as Tottenham Hotspur and Juventus have reignited their interest for Milik, with Roma looking for a replacement for Edin Dzeko.If Milik wants some stability in his career after enduring a torrid time at Napoli and if Marseille are ambitious enough, a permanent move could be beneficial for all parties involved.#2 Juan Foyth (Tottenham Hotspur/ Villarreal)Juan Foyth in action for VillarrealJuan Foyth has been an integral part of Unai Emery's Villareal, who recently beat Manchester United on penalties to win the Europa League.The Argentine played a key role in keeping Marcus Rashford quiet and managed more tackles than any other player on the pitch in the Gdansk final. He completed six tackles despite missing several games leading up to the final because of injury.Foyth has been excellent for Villarreal since arriving from Spurs on loan ahead of the 2020-21 season. He initially played as a holding midfielder before coming into his own as a right-back. He was also deployed as a centre-back.CAMPEONES!!! ⚽️🥇🏆 @europaleague @villarrealcf pic.twitter.com/L62x44G769— Juan Foyth (@JuanMFoyth) May 27, 2021Despite playing in multiple positions, the Argentine registered a tackle success rate of 70%. For context, Spurs right-back Serge Aurier only completed a 65% tackle success rate.Considering his impressive performances while on loan, Villarreal are reportedly ready to exercise the £12.8 million option to buy Foyth and make his loan deal permanent.Foyth has proved capable of starting for Tottenham Hotspur. But it looks likely that the London club may be unable to stop him from joining Villareal on a permanent basis.