As others put he's probably going to be put into LM.
Given he didn't sign for Man U probably because they couldn't garentee him games there, even though with heinze's future in doubt which would mean he'd only be competing with Evra, I'd doubt he'd of signed if he thought he was going to have to compete with two LB's.
From what i hear he is a very attack minded player with a brilliant left foot, so maybe the perfect combination with lennon on the other side, who knows! and given that he's also acclaimed for his defensive skills will provide good support for Lee or AE, Lee's performances were getting better and better and with good support i think him and AE can really develop. Perhaps he was the better option over Baines for this reason, he may yet solve two problems in one (which would be handy!) only time can tell.