Assulin was born in Nahariya, Israel. He started his career in the football school of Hapoel Haifa. In 1999, at age seven, he moved to the Beitar Tubruk youth ranks. In 2003, when he was just 12, Shlomo Scharf, his team coach, proposed to Assulin's parents to consider taking their young prospect to try out for FC Barcelona, where he was accepted into the youth ranks.
Club career
Barcelona
In August 2007, Assulin graduated to the FC Barcelona B team, and was offered a new contract, a senior contract for another three years and a €20 million buy-out clause. At the end of the 2007–08 season, Barcelona B won the league title with 83 points, and the manager, Pep Guardiola, was promoted to the job of senior team manager. Assulin was rumored to be one of the players that Guardiola would promote to the first team. After missing most of the 2008–09 season due to injury, Assulin received an invitation to participate in pre-season matches with the Barcelona first team. He made his debut first-team start in a competitive match of the Copa del Rey against Cultural Leonesa on 28 October 2009, before being replaced by Eric Abidal after 56 minutes. Due to the lengthy 2009–10 season, many Barcelona players were given breaks towards the end of the year, so on 29 December 2009 Guardiola brought in Assulin and his teammates Víctor Vázquez, Thiago and Jonathan dos Santos. On 1 July 2010, Assulin and Barcelona parted ways by mutual consent. They offered him a three-year contract but as they could not offer him a guaranteed first-team squad position and instead sought to develop him at Barcelona B, he refused the offer. Assulin also had a complicated relationship with the manager of Barcelona B, Luis Enrique.
Manchester City
On 14 December 2010, Assulin joined Premier League club Manchester City on a two-and-a-half-year deal. He spoke of his wishes to partner his former Barcelona teammate Yaya Touréat the club. The early part of 2011 saw Assulin make his City Reserve squad debut against Newcastle United, coming on as a second-half substitute in a 5–1 win. On 17 November 2011, Assulin declared that he was prepared to be loaned out from Manchester City in order to receive first-team action. He had so far failed to receive a call-up from first-team manager Roberto Mancini but was too old to play in the inaugural under-19 NextGen series with the City Elite Development Squad, restricting him to playing occasionally for the Reserves. Assulin said: "I need confidence and I can only get that by playing regularly. City and I both feel that I should go out on loan so I can play every week. I could stay in England or maybe join a team in the Spanish second division". Six days later, Championship side Barnsley announced that they had agreed a loan deal until 3 January 2012, with their manager Keith Hill saying that he was impressed by his performance for Israel under-21 against England at the club's Oakwell ground that September. After fitness issues came up, the deal collapsed. On 9 February 2012, Assulin scored for the Manchester City Elite Development Squad in their 4–2 derby win over rivals Manchester United. He entered the Manchester Senior Cup tie at half-time as a substitute for Denis Suárez, and scored their 2–2 equaliser in the 65th minute and he also assisted for the fourth goal in stoppage time. Eight days later, Assulin, along with fellow City youngster Abdul Razak, joined Championship side Brighton & Hove Albion on an initial one-month loan until 19 March, but with the option to extend this by two months. Manager Gustavo Poyet described the loan move for Assulin as a "no-brainer" and a "unique opportunity." Assulin made his Brighton debut on 22 February against Hull City, coming on as a substitute for Razak in the 77th minute of their 0–0 draw. He made his first start against Cardiff City on 7 March and was substituted after 59 minutes of a 2–2 home draw. On 19 March, after one start and three substitute appearances, Brighton exercised their option to extend Assulin's loan deal until the end of the season. Assulin was released from Manchester City on 22 May 2012, alongside Owen Hargreaves.
Later career
On 11 July 2012, Assulin signed a one-year deal with recently relegated Racing de Santander. Six days later, he was introduced as a player in a press conference. On the opening game of the season on 19 August, he made his debut in a 1–0 loss against Las Palmas; he soon scored his first goal, on 15 September, in a 3–0 win over Recreativo de Huelva, giving the club their first win of the campaign. On 5 July 2013, Assulin signed a three-year deal with Granada CF, being immediately loaned to Segunda División's Hércules CF in a season-long deal. He appeared regularly for the Valencian outfit, which were relegated after finishing dead last. In his second game, a goalless draw at CD Tenerife on 25 August, he was sent off for kicking out at Carlos Ruiz. On 15 August 2014, Assulin signed a two-year deal with RCD Mallorca, also in the second level. In October 2015, free agent Assulin trialled with Rangers of the Scottish Championship; Manager Mark Warburton was not sufficiently impressed to offer him a contract. After a brief spell at Hapoel Tel Aviv – his first experience of the Israeli Premier League – he went back to Spain to sign for CE Sabadell FC in the third tier on 10 August 2016. He departed the Catalan club in January 2018 after his contract was terminated by mutual consent. On 13 February 2018, Kazakhstan Premier League side FC Kairat announced the signing of Assulin on a two-year contract. On 30 March, it was cancelled by mutual consent. On 26 September 2019, Assulin signed a two-year contract with Liga I club Politehnica Iași.
International career
Assulin was called up by the Israeli national football team for their friendly match against Chile in 2008. He debuted for Israel as a substitute in the 78th minute of the friendly, 14 days before his 17th birthday. By playing in this match, he broke Ben Sahar's record for youngest national team debut by 195 days. He went on to represent the Israeli under-21 national team in preparation at the 2013 UEFA European Under-21 Football Championship, hosted in the country.
