A section of Manchester United fans online were not too happy to see Cristiano Ronaldo get substituted off during their 3-1 win over Brentford.With a 2-0 lead going into the final 20 minutes, Ralf Rangnick decided to take Ronaldo off and replace him with Harry Maguire to protect the lead. United were in a similar position against Aston Villa at the weekend when they squandered a two-goal lead. Cristiano Ronaldo was unhappy after being taken off on the 71st minute mark.Despite Rangnick making a bold move for the betterment of the team, a portion of United fans did not like his decision. Some fans were not happy to see Maguire get on the pitch, while others credited Ronaldo's attitude for not wanting to leave.Here are some of the best tweets from Manchester United fans in this regard:The Tactical Times@Tactical_TimesCristiano Ronaldo is replaced by Harry Maguire as punishment for saying he didn't sign for United to finish 6th3:01 AM · Jan 20, 2022736Cristiano Ronaldo is replaced by Harry Maguire as punishment for saying he didn't sign for United to finish 6thMike@MikeLUHG0Ronaldo subbed off for Harry fucking Maguire. You won't see a worse sub in football history. Hope this helps3:00 AM · Jan 20, 20221937302Ronaldo subbed off for Harry fucking Maguire. You won't see a worse sub in football history. Hope this helpsTCR.@TeamCRonaldoBrentford's manager Thomas Frank was all of us when Cristiano was subbed. 🙃4:34 AM · Jan 20, 20221182104Brentford's manager Thomas Frank was all of us when Cristiano was subbed. 🙃 https://t.co/QiZHDVFZ45Rashbonlahor@rashbonlahori@MikeLUHG0 That is shocking. Feel sick3:01 AM · Jan 20, 20223@MikeLUHG0 That is shocking. Feel sickClyde Tlou@clydegoalIf I was Ronaldo, I would have been angry too. Imagine being subbed for Maguire11:00 AM · Jan 20, 20221If I was Ronaldo, I would have been angry too. Imagine being subbed for MaguireKtorum 🔴⚫️@KjellCaramellMaguire just irritates the hell out of me!No wonder Ronaldo got grumpy being subbed for him!10:01 AM · Jan 20, 20221Maguire just irritates the hell out of me!No wonder Ronaldo got grumpy being subbed for him!Shreyas🔰@Shreyas_56@ManUtd Disrespectful to remove ronaldo3:01 AM · Jan 20, 202244@ManUtd Disrespectful to remove ronaldoKaz.@Kaz7iiRonaldo's mad about being subbed off & rightly so, that too for HARRY MAGUIRE 3:07 AM · Jan 20, 20221194Ronaldo's mad about being subbed off & rightly so, that too for HARRY MAGUIRE 💀 https://t.co/6C4S53vMriHM@MUnitedGirlRonaldo is fuming for being taken off love that about him! 36, WON IT ALL and still hungry 3:02 AM · Jan 20, 202218127Ronaldo is fuming for being taken off 😂 love that about him! 36, WON IT ALL and still hungry ❤️Andrew #GlazersOut@Glazers_Out2018I love Ronaldo is pissed getting taken off. That’s the mentality Utd need.3:01 AM · Jan 20, 2022173I love Ronaldo is pissed getting taken off. That’s the mentality Utd need.Charlotte Duncker@CharDunckerRonaldo not letting it go. Asking those on the bench why he was the one to be taken off.3:02 AM · Jan 20, 202215219Ronaldo not letting it go. Asking those on the bench why he was the one to be taken off.Floki@jabsilsRonaldo just came back from a muscle injury, he must understand why he’s being taken off 🤦🏾‍♂️3:01 AM · Jan 20, 202281Ronaldo just came back from a muscle injury, he must understand why he’s being taken off 🤦🏾‍♂️It is worth mentioning that Ronaldo had missed United's last two matches in all competitions after suffering a hip injury. This could have been one of the reasons why Ralf Rangnick decided to take the 36-year-old forward off in the second half.Manchester United secured a 3-1 win over Brentford to become the first Premier League team to win 300 away matches. Goals from Anthony Elanga, Mason Greenwood and Marcus Rashford were enough to secure all three points for the Red Devils.Cristiano Ronaldo, meanwhile, has now gone two consecutive matches without scoring a league goal. The five-time Ballon d'Or winner also failed to score against Wolverhampton Wanderers at Old Trafford.Cristiano Ronaldo's fitness is vital for Manchester United for the remainder of the seasonManchester United will need to do everything they can to maintain Ronaldo's fitness as they head into the busy second half of the 2021-22 season. The 36-year-old forward is currently the club's highest goalscorer, having scored 14 goals in 23 outings in all competitions this season.Bruno Fernandes, who is United's second-highest goalscorer this season, has only scored half of Ronaldo's tally.Cristiano Ronaldo, however, has amazing fitness levels despite his age. The 36-year-old forward has so far only missed one league game through injury. Out of the 17 league appearances, Ronaldo has completed the full 90 minutes on 12 occasions.Cristiano Ronaldo@Cristiano3 important points! well done lads 🏽🏽4:08 AM · Jan 20, 2022158714110403 important points! well done lads 💪🏽👏🏽 https://t.co/nzPNhrdIAiManchester United have a vital game against West Ham United at the weekend. The Hammers are currently fourth in the Premier League standings and occupy the final Champions League spot.The Red Devils will also need Cristiano Ronaldo to be fully fit when they take on Atletico Madrid in the Round of 16 of the UEFA Champions League on February 23. The five-time Ballon d'Or winner has scored six goals in five group matches this season.