Manchester United left Ole Gunnar Solskjaer's squad short due to the club's dealings in the transfer market, says Bryan Robson.
Defeat away to Newcastle United last time out left the Red Devils 12th in the Premier League table, two points above the relegation zone.
Solskjaer has overseen a poor run of form since his March appointment on a permanent basis, a period in which United have taken 17 points from 16 league games.
His squad was bolstered by Harry Maguire, Daniel James and Aaron Wan-Bissaka, but senior players including Romelu Lukaku, Alexis Sanchez, Ander Herrera and Chris Smalling have departed.
Robson, who captained the club and won two Premier League titles with United, feels the transfer business was inadequate but, asked if United should stick with Solskjaer, he said: "Yes, I do.
"Because everyone went with the policy that they want to encourage the young boys coming through the ranks. That's exactly what United have done.
"I think they've maybe allowed too many good, experienced players to leave the club without replacing them. That's why it's left them a little bit short."
United have particularly struggled for goals since a 4-0 home win against Chelsea on the opening weekend of the Premier League season.
England striker Marcus Rashford netted twice in that victory but he has only scored once for club and country since, a run that has seemingly hit his confidence.
Robson, speaking at a Football Writers' Association dinner sponsored by William Hill, feels there are aspects of his game where the 21-year-old must develop.
"I think he has still got a little bit of knowledge to know about being a centre-forward," Robson added. "I think it's a natural game for him coming off the left side but the right side as well.
"But I think going through the middle of the park, I think Marcus needs to know the game that little bit better where it's not always about running through, it's about build up play and bringing midfield players into the game.
"That's where Marcus can maybe improve his game a little bit."