Barcelona kicked off their 2020-21 La Liga campaign with a resounding 4-0 victory over Villarreal. Lionel Messi followed up Ansu Fati's brace with a goal from the spot before Pau Torres' own goal put the result beyond doubt at the stroke of half-time.Now, on paper, travelling to take on a club that escaped relegation by the skin of their teeth last season should seem like easy work for Ronald Koeman and co. However, this is a fixture that has proved to be a lot more testing than most for Barcelona.On that note, let's take a look at five reasons why Barcelona are set to have a tough time against Celta Vigo tonight.#5 Absence of key players will reduce bench strengthJunior Firpo is likely to miss out as he is nursing a hamstring issueAs per the latest reports, Junior Firpo is likely to miss out due to a hamstring issue. Samuel Umtiti continues to be sidelined and Marc-Andre ter Stegen is a long-term absentee. Neto has been guarding the sticks for the Blaugrana so far.Junior Firpo's absence will reduce the number of options at Koeman's disposal as well. To make things worse, Ousmane Dembele is currently linked with an exit with various reports claiming that Barcelona are also keen on sending him away to furnish funds and make way for the arrival of Memphis Depay from Olympique Lyon.With only a few days remaining in the transfer window, Manchester United have now been linked with Dembele and the ongoing saga might unsettle him. If that's the case then Barcelona will have to do with a bench that they is far too short on experience to make a difference when called upon.The squad for #CeltaBarça! pic.twitter.com/dremKgyk5w— FC Barcelona (@FCBarcelona) September 30, 2020#4 Barcelona's awful away form and Celta Vigo's green patchBarcelona v Bayern Munich - UEFA Champions League Quarter FinalBarcelona won their first match at home quite comfortably against Villarreal. That's not unusual because the Catalans have been pretty good at the Camp Nou. However, they have kept an awful away record ever since the days of Ernesto Valverde.Despite the lack of crowds and the hostile atmospheres at away fixtures in the Covid landscape, the Cules have struggled on the road. They have, time and again, failed to take the lead in games away from home and whenever they have, they have struggled to keep it.Meanwhile, Celta Vigo are unbeaten in three games so far this season and have beaten Valencia at home already. Celta Vigo have now gone four games unbeaten in the La Liga and that's their second longest undefeated run in the last three seasons.#CeltaBarça incoming💪🔵🔴 pic.twitter.com/tkFD5DQ8wk— FC Barcelona (@FCBarcelona) September 30, 2020