Manchester United vs Arsenal is obviously no longer the game it once was in the Sir Alex Ferguson - Arsene Wenger era, but the fixture is still a Premier League classic. The stars may not shine as bright now, but the emotion and passion of fans on both sides when it comes to the game remain undiminished.When Ole Gunnar Solksjaer and Mikel Arteta take to the touchline at Old Trafford on Sunday night, they will only battle it out as the respective 11th and 15th-placed sides in the 2020-21 Premier League table.It's amply clear that it has not been a comfortable start for either side this season. That makes the three points on offer all the more crucial for both Manchester United and Arsenal, who will want their star players like Pierre-Emerick Aubameyang, Paul Pogba and Marcus Rashford to continue their fine recent form.On that note, here are five players to watch out for during this titanic clash:#5 David de Gea (Manchester United)Manchester United goalkeeper David de GeaPlenty of pundits had written off Manchester United's David de Gea after a couple of seasons where he looked mediocre at best. However, the Spaniard has hit back resoundingly at his critics, doing all of his talking on the pitch as he seems to have got back to his best this season.The fierce competition provided by Dean Henderson has ensured that the Manchester United number one has been on his toes, with the Spaniard putting in a string of impressive displays of late.Foremost amongst those was his display against Paris Saint-Germain in the UEFA Champions League, where he was pivotal in Manchester United's 2-1 win at the Parc des Princes. He pulled a string of saves in that game, the pick of them coming against Kylian Mbappe.It was classic De Gea as he pulled off a near-impossible save just when it seemed that the young Frenchman would curl one into the Manchester United net.Peak @D_DeGea ❤️#MUFC #UCL pic.twitter.com/L1F1dDjXwL— Manchester United (@ManUtd) October 28, 2020When it comes to Arsenal, De Gea tends to turn into an invincible beast. Who can forget his record-equalling display in 2017, when he denied Arsenal an incredible 14 times to give Gunners fans recurring nightmares?David de Gea’s record 14 saves against Arsenal equalling the record for most stops in a Premier League match in 2017!Single-Handedly kept us in the game in a 3-1 Win 🧤 pic.twitter.com/3gg2eLad0q— United Zone (@ManUnitedZone_) October 31, 2020The fact that De Gea looks like he is back to his best ought to perturb Arsenal fans no end. The Gunners have a terrible recent record at Old Trafford. To make matters worse, they now have to contend with a player who could thwart their misfiring attack, which doesn't augur well for their prospects in the game.#4 Thomas Partey (Arsenal)Arsenal's latest recruit Thomas ParteyThe quality and big-game pedigree of Thomas Partey is in little doubt; the Ghanian has arrived at Arsenal after a bevvy of impressive displays for Atletico Madrid in the biggest of games.If Arsenal fans had any qualms about their club spending €50 million on Partey, they were swiftly put to rest when the player put on an impressive debut performance against Rapid Wien in the UEFA Europa League.Comments on Thomas Partey last night:Mikel Arteta: "He was fantastic."Owen Hargreaves: "It was one of the best debuts I've ever seen."Martin Keown: "He oozes class." pic.twitter.com/piE6GtNtOJ— AFTV (@AFTVMedia) October 23, 2020However, in typical Arsenal fashion, Partey had his critics in the Gunners' loss against Leicester City. But these 'critics' had conveniently ignored the fact that Granit Xhaka and co decided not to pass the ball to the player in the second half, resulting in a visibly frustrated Partey looking rather isolated.At Old Trafford, the Ghanian will be tasked with shadowing Manchester United's Bruno Fernandes and Paul Pogba - a tall task for any midfielder. It will be interesting to see how Mikel Arteta uses his undoubtedly talented midfielder, who has the capability to shut down the very best.