The 24-year-old Moroccan international's deal with Ajax collapsed due to his wage demands, which allowed Liverpool to hijack the deal.
Here's what you need to know about Brendan Rodgers' newest signing.
It's a pleasant surprise to see Liverpool conduct their transfer business behind closed doors. No major media outlet or twitter ITK reported the signing before the club, which is how it should work.
There are two explanations for the Trojan horse-like signing of Oussama Assaidi.
1. Chris Bascombe at The Telegraph reported that Liverpool were chasing Barcelona's Cristian Tello.
2. De Telegraaf (via goal.com) said Assaidi had agreed terms with Ajax.
Was he really going to turn down Ajax? Of course not. With the benefit of 20-20 hindsight, Ajax should have taken Assaidi's threat more seriously:
Let's cut to the chase, I want to earn a good salary. I know that Ajax have a new policy, but I will stay at Heerenveen unless they offer me a good salary. I still hope to reach an agreement with Ajax, though.
How good is Assaidi? Read on to find out.
1. Luciano Narsingh: One of the most dynamic players in Europe right now. Can beat full-backs with his incisive crossing but can also go past defenders with ease. Is such a dominant an attacking player that he probably has sent a few left-backs to the psychiatrist's couch. Secured a €4.1 million move to PSV Eindhoven, which should allow the club to sell him for a massive profit like they did with Ronaldo and Ruud van Nistelrooy.
2. Bas Dost: Excellent goal poacher but heavily reliant on selfless and productive teammates. Doesn't have the finishing ability of Klaas-Jan Huntelaar let alone Afonso Alves. Dost recently signed a five-year contract with Wolfsburg.
3. Filip Djuricic: Majestic playmaker, whose upside is just as high as Christian Eriksen.
4. Daryl Janmaat: Such a solid right-back and Heerenveen clearly missed his influence at full-back because Doke Schmidt wasn't good enough when he filled in. The readers of Voetbal International voted Janmaat into the right-back position for the Eredivisie Team of the Year. Janmaat returned to boyhood club Feyenoord on a Bosman.
5. Oussama Assaidi: For someone so gifted, he left a lot to be desired. Tricky and fleet-footed inside-out forward, who was hot and cold on the left.
1. Dries Mertens: Has such a monopoly over Eredivisie defences that he could score even if he was playing at 50 percent. He memorably ran into a moving brick wall that was Ricardo van Rhijn in a 2-0 loss to Ajax. It was astonishing to see a rookie right-back suffocate the Eredivisie's best attacking player. Mertens and Luciano Narsingh will be the Eredivisie's most productive and feared tandem wide forward combination.
2. Ola John: So quick, so dangerous cutting in and has world-class potential. Benfica snapped him up for €9 million. Cannot afford to rest on his laurels like his brother, Collins John.
3. Dusan Tadić: Has splendid dribbling ability an eye for the incisive pass. Will become a household name at Twente.
4. Oussama Assaidi: Elite one week, missing the next week. Tore VVV-Venlo's back-line apart with a hat trick of assists but was anonymous in a 5-0 loss to Ajax and a 5-1 loss to PSV Eindhoven.
Signing Heerenveen's fifth best player isn't exactly ideal but he only cost Brendan Rodgers £2.4 million. It's low-risk, high-reward as opposed to signing Stewart Downing for £20 million.
Oussama Assaidi's talent is there but the production isn't. He may have been the Eredivisie's fourth best left-sided attacking player last season, but there is a clear gap in quality between him and Dries Mertens.
Football writer Leander Schaerlaeckens tweeted:
For those asking, Oussama Assaidi is classic Dutch scoring winger. R-footed, can play on both sides. Good crosser from R,takes on men from L.
On the left, Assaidi will leave you wanting more, so Rodgers should play Assaidi on the right and see what he produces. Last season, he was denied the chance to play there because of Luciano Narsingh's excellence.