They are joined by English firms Eversheds and Optima, with all four selected to provide a range of restructuring and insolvency work on behalf of the bank.
A Clydesdale spokesman said: "The bank has strong relationships with each and looks forward to continuing to work closely with these firms."
The latest announcement comes less than a week after it emerged that Harper Macleod and Morton Fraser were among the firms which were cut from the revamped national panel recently announced by Clydesdale.
Clydesdale also has a business and private banking panel, which has regional elements within it, and a retail panel.
Harper Macleod and Morton Fraser both confirmed yesterday they would also provide services for the business and private banking panel, which had been re-tendered in recent months.
That is likely to include work for the bank around small and medium enterprise customers as well as larger corporate clients across central Scotland.
Martin Darroch, chief executive of Harper Macleod, said: "We are delighted to be extending our reach in the services we provide to Clydesdale Bank, a key client of the firm with which we have a longstanding and extremely strong relationship."
Bruce Wood, partner at Morton Fraser, said the appointments were a "welcome endorsement" for the firm and cemented its existing relationship with Clydesdale.