Newly appointed Manchester United manager Ruben Amorim has been sent a warning about taking up the job at Old Trafford.
The Portuguese tactician will officially start his reign at the Red Devils on 11 November after penning a three-year contract.
Read: Man Utd Announce New Manager!
While there may be a fresh start under the new coach, Carragher has warned Amorim it will take a while to see if he can succeed, citing Jose Mourinho and Ole Gunnar Solskjaer.
"Amorim will undoubtedly generate a short-term, feel-good factor, too. New United managers are welcomed like a breath of fresh air and there is not a lot of work needed to make the team massively improve very quickly... Amorim's real challenge will be in 18 months' time – just as it was for those who left Old Trafford believing they needed more time and patience to get it right.
"That is when clearer assessments will be made as to whether he is creating a side that has the consistency to actually win the title and Champions League. That is the currency United managers must deal in – the standard against which Manchester United will and must always be judged.
"Faith in Mourinho, Solskjaer and Ten Hag evaporated because after a couple of seasons each, fans and media were scrutinising the team and making what has become the cliched observation that they were still five years away from reaching Manchester City's level.
"It will take a while before we can know if Amorim can succeed where his recent predecessors were found wanting. He is clearly a highly rated coach who has been on the radar of top clubs for a while."
Interim manager Ruud van Nistlerooy is set to take charge of the team for the next two Premier League matches.
