The duo both went out on loan last season and learned a lot at Wigan and Sunderland respectively.
Cleverley made a name for himself at Wigan where he helped them escape the drop on the last day of the season at Stoke while Welbeck scored six goals in 26 Premier League appearances for Sunderland.
Both players have now joined up with the rest of the United squad in the United States having been given extra time off to recuperate after the U21 European campaign.
"They won't go on loan again," the United boss confirmed.
"Going on loan only serves one purpose; keeping them happy by playing all the time.
"At their ages, it wouldn't do us any good because other clubs would be benefiting from what we could be benefiting from.
"Because of the experience they have had, keeping them now benefits us."