Louis van Gaal has hinted that he will need to sign more wing-backs for his new-look Manchester United squad.
The Dutchman has introduced the 3-4-1-2 system he also played with Netherlands at the World Cup during United's preseason fixtures on their U.S. tour.
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And though United have paid 27 million pounds for Luke Shaw, experienced alternatives as left wing-backs after both Patrice Evra and Alexander Buttner have been sold, with the untried Reece James featuring in the matches against LA Galaxy and Roma.
Right-back Rafael da Silva, who has returned to England from the World Cup with a groin injury, and winger Antonio Valencia have been used on the other flank while Ashley Young had to be pressed into emergency service as a right wing-back in the second half against Roma.
And Van Gaal suggested that even if he reverts to the 4-3-3 formation he has used for much of his managerial career, he still needs more options on the flanks.
"I don't buy players for [the sake of] buying players," he told Sky Sports. "I buy players to improve my selection. First I have to see what we need in all the positions from the system we shall play. When we play 4-3-3 I shall use more or less the same players but 4-3-3 I need more specialists on the wings and more attackers."
Van Gaal explained the change of shape as a response to the players at his disposal after fielding Juan Mata behind two strikers in United's first two friendlies.
He added: "With this system I at least two strikers can play and at least the No. 10 can play and also the two [central] midfielders so the specialists are the wing-backs.
"I am more in favour of a 4-3-3 formation that also Sir Alex [Ferguson] has played but I think with the selection now, I have to choose this system."
Van Gaal has been linked with Ajax's Daley Blind, who operated as a left wing-back in the Holland team he led to third place in this summer's World Cup.
Defender Chris Smalling revealed he has enjoyed Van Gaal's new formation, saying at a news conference in Washington: "If anything I like this more than the traditional 4-4-2 because it gives us more freedom to go in and be aggressive."