I mean lenders just want repayment
Yes and, for the purposes of mitigating risk, suitable collateral. In United's case, the club would be unable to service a debt of, say, £3bn+ from its operating cash flow and any lender would probably rather have the debt collateralised against Ineos' assets, since the company is significantly larger and more valuable than Manchester United. To answer your question, Ineos could therefore probably get away with transferring some but not all of the acquisition debt obligation to United, if they wanted to.