Evra has suffered a dip in form since the 2010 World Cup, and at a certain point, it is no longer just a temporary loss of form. Each error reinforces the possibility that Evra is now past his sell-by date.
The Frenchman is a constant presence in the United team, and rarely has another player gotten a chance to prove themselves at left back in the past five seasons.
While it becomes increasingly clear that a new left back is needed, there remains the question of who should replace Evra.
These five players would all be excellent (and realistic) replacements for Evra as left back for United.
Fabio da Silva is first on the list to replace Patrice Evra at left back if Manchester United promote from within.
While his twin brother Rafael has already been heavily involved in the first team at right back, Fabio has struggled to get into the team.
In four seasons at Old Trafford, Fabio has made just 50 appearances for the club. This is primarily due to his susceptibility to injury. Much of his time in England has been spent in the treatment room, and that hindered his chances to fully establish himself in the first team.
Despite the injuries, however, Fabio has played in big games for United. With his brother sidelined by injury last season, Fabio regularly played at right back during the final months of the 2010/11 season. His performances deputizing for his brother ultimately earned him a spot against Barcelona in the 2011 Champions League Final.
Fabio still has plenty of room to improve defensively, but time in the first team should encourage that development. Although Fabio still has some shortcomings as a defender, given some of Evra's performances this season, it's hard to imagine Fabio could do any worse.
He provides an attacking threat from the left back position. As is common among Brazilian full-backs, Fabio is excellent going forward and has even featured for United as a winger on occasion.
However, United supporters are concerned with Fabio's endurance and recklessness. The 21-year-old rarely lasts a full 90 minutes and is prone to poor tackles, resulting in discipline or self-induced injuries.
With the January transfer window recently closing, Sir Alex Ferguson will have to make due with what he has. If Evra is rightfully dropped, then Fabio must surely be first in line to replace him.
Zeki Fryers made his first team debut for Manchester United this season in the Carling Cup against Leeds United and has since become more involved with the first team.
Fryers made his Champions League and Premier League debuts this season as well, suggesting Sir Alex Ferguson has big plans for him in the first team.
Although Fryers spent much of last season on the sidelines due to injury, he was involved later in the season as part of the side that won the 2010/11 FA Youth Cup.
He got off to a promising start this season with the Reserves and was rewarded with an opportunity to stake his claim in the first team. In his six senior appearances this season, Fryers made the most of his opportunities and impressed at both center back and left back.
Although some may raise concern over his inexperience, Fryers appears composed in the defense and slots in seamlessly with the established defenders. To play in the United defense at 19 years old and not look out of place speaks highly of his ability.
Recent transfer speculation has linked Fryers with a loan move to Burnley. This could be brilliant for his progress at Old Trafford. After a few months of experience in the Championship, a push to take the left back spot from Patrice Evra next season could be on the cards.
Jordi Alba made the breakthrough with the Spain national team earlier this season, and Manchester United would be wise to secure the promising young left back before Spanish giant Barcelona swoop in.
Alba has been heavily involved at Valencia the past three seasons with 117 appearances, contributing eight goals and six assists. The 22-year-old has experience in the Champions League with Los Che and would offer a great long-term option for United.
Capable of playing as a left winger, Alba provides versatility. He is skilled both defensively and in attack and could fill in as a winger if United were facing an injury crisis like the one they've experienced this season.
On his debut for Spain in October 2011, Alba chipped in with an assist during Spain's 3-1 victory over Scotland. Many have tipped him to be the future left back for the reigning World champions.
If United decided to pursue an alternative to Patrice Evra, Alba is a very talented up-and-comer worth looking at.
Emilio Izaguirre claimed Manchester United were interested in him last summer, and Sir Alex Ferguson should look to revive that interest at the end of the season.
Izaguirre joined Celtic in August 2010 and was quick to establish himself as one of the best players in the Scottish Premier League.
In his debut season, Izaguirre was awarded SPFA Players' Player of the Year, Clydesdale Bank SPL Player of the Year, Celtic Players’ Player of the Year and Scottish Football Writers Player of the Year.
Along with being a very good defender, Izaguirre is a fantastic attacking threat. He is very fast and a good passer as well, often providing excellent crosses from the left wing. In this way, he provides a similar attacking threat to Evra, although he does not get caught out of position as often as the Frenchman.
Izaguirre is only 25 years old, but with 45 appearances for Honduras, he has plenty of experience. One criticism is that, while he has become a star player, he has done so in a weaker league. Nevertheless, his superb performances suggest he might be worth a gamble.
A broken ankle in August 2011 left Izaguirre sidelined until January 2012. Although he has reestablished himself in the Celtic team, it will be interesting to see if the injury has any negative effects on his performances.
If he continues to play at the level he did prior to the injury, however, Izaguirre is certainly an option to take over as left back for United.
Leighton Baines is one of the best left backs in the Premier League, and he would be the ideal player to replace Patrice Evra at Manchester United.
Last season, Baines played every minute of every game for Everton in the Premier League. He was, and still is, the most valuable player in David Moyes' side. For his performances in 2010/11, Baines was awarded both Everton Player of the Season and Everton Players' Player of the Season.
He is a very good defender and also provides an attacking threat from the left back position. In the 2010/11 season, Baines had 11 assists for Everton—more than any other defender in the league. He also scored seven goals for the club, with his strike against Chelsea in the FA Cup earning him Everton Goal of the Season.
Baines should be the first choice to replace Evra at left back at Old Trafford. At the age of 27, Baines is both experienced and proven in the Premier League. He would provide a good defensive presence at left back, which Evra has struggled to fill, while also contributing substantially to the attack.
Moyes is unlikely to easily part with his star player, but United should still be able to secure the signing of Baines for a reasonable fee. After establishing himself as one of the Premier League's finest with Everton, now may be the perfect time to move to a club challenging for the title.