[1] A product of Zürich academy, Gashi made his professional debut at the age of 18 on 12 August 2006 in the 2006–07 Swiss Super League match against St. Gallen, playing in the last 13 minutes of the 3–1 loss.

[2] He also made his European debut later on 6 December of the following year, appearing as a substitute in an UEFA Cup group stage match against Spartak Moscow which finished in a 1–0 away loss.

[3] On 29 January 2008, in the winter transfer window, Gashi was sent on loan to Swiss Challenge League side Schaffhausen until the end of 2007–08 season.

Gashi made his Bellinzona debut on 23 July 2008 in the Swiss Super League match against Neuchâtel Xamax, playing for 65 minutes in a 1–2 home defeat.

[6] He scored his first league goal of the season on 5 October during the 3–3 away draw against the same opponent, which was followed by another strike in team's 2–3 home defeat to Basel.

[7][8] He finished his first season with Granata having made 24 appearances in all competitions, including 17 in league and 5 in UEFA Cup, scoring three goals in the process.

Gashi started his second Bellinzona season on 12 July 2009 by playing in the opening league match against Neuchâtel Xamax, finished in a 1–1 draw.

In January 2010, Gashi joined fellow Swiss Super League side Neuchâtel Xamax, signing a two-year contract.

[17] He was allocated squad number 10, and made his competitive debut on 15 July in the opening league match of 2012–13 season against Sion, finished in a 0–2 home defeat.

[22] Gashi played full-90 minutes in both legs of UEFA Champions League third qualifying round against Lyon, who eliminated Grasshopper by winning both matches 1–0.

[28][29] He continued with his solid performances by netting another goal in the 2–0 win at Lausanne which ranked him first in the top goalscorers list among with his teammate Caio.

[36][37] On 28 June 2014, the UEFA Champions League hopefuls FC Basel 1893 reached an agreement with domestic rivals Grasshopper to sign Gashi on a four-year contract in the next coming days subject to passing a medical.

Gashi made his competitive debut for the team on 19 July 2014 in the match against Aarau, starting and providing the goal of Naser Aliji in an eventual 2–1 away win.

[44][45] He continued with his solid performances in league, supplying two assists in the 3–1 home win against Young Boys, which was followed by the lone goal scored against the same opponent on 18 October.

In the description for the Albanian player, the UEFA website said that Gashi ran about 12 km, making it the biggest threat to "Reds" doing 2 solo-actions (one blocked and one outside the gate) were the best argument for the 26-year-old qualities.

[58] He became 1 of the 3 Albania international footballers which participated in a knockout stage of the UEFA Champions League for the first time in history, among his teammates at Basel Taulant Xhaka and Arlind Ajeti.

[66] During the season's winter break, on 1 February 2016, Basel announced that Gashi was leaving the club and had signed a four-year contract with Colorado Rapids.

[69] He experienced what was considered a good first season with the Rapids, scoring 10 league goals as he led the team to a 2nd-place finish in the Western Conference, and a long playoff run.

[70] On 28 May 2017 Gashi provided an assist for the Kortne Ford goal which gave Colorado Rapids the 1–0 victory over Sporting Kansas City.

[74] Gashi was part and capped for the Switzerland U-17, U-19 and U-21 teams in competitive youth UEFA European Championships respective age categories.

Then he was an unused substitute in 2 next matches against hosts France where they lost 2–0 and against Romania in an Albania's historical 1–0 win with a goal scored by Armando Sadiku.