Alexis Sanchez will struggle to hit the same heights for Manchester United as he did at Arsenal, according to former Liverpool player Dietmar Hamann.
Jose Mourinho swooped for the Chile international in January in exchange for the out-of-favour Henrikh Mkhitaryan.
The move is yet to pay dividends, with 29-year-old Sanchez having only scored once in eight competitive appearances during an underwhelming start to life at Old Trafford.
And former Reds midfielder Hamann believes the all-action forward's best is behind him.
"I'm not sure whether he has got the impact he had got three years ago," he said.
"I think he's in his late twenties now, he is a very physical player, you have to see how long he can play at a very good level or the top level.
"And I'm just not sure whether he is the same player that he was when he first came to Arsenal."
Sanchez will have the chance to prove Hamann wrong when United host an in-form Liverpool on Saturday.
Hamann, who spent seven years on Merseyside, expects a similar contest to the 0-0 draw the teams fought out in October.
"I think it'll be a low scoring affair again, because in these big games Mourinho doesn't want to commit players forward," the ex-Germany international said.
"Liverpool has to be patient, I think we saw a 0-0 earlier in the season at Anfield, I would probably go for the same score again."
Dietmar Hamann was speaking on behalf of TAG Heuer to promote the TAG Heuer Premier League Pressure Test (http://tagheuerpressuretest.com/). TAG Heuer is the Official Timekeeping Partner of the Premier League