June 13 (Reuters) - An investor in Diversified Healthcare Trust on Tuesday expressed concerns about the "accumulation" of the real estate investment trust's (REIT) shares by the chief executive of the company that manages the firm.

Flat Footed, which holds about a 9.7% stake in DHC, called on the company's board to assess "whether it is appropriate for (Adam Portnoy) to continue buying shares."

Portnoy leads RMR Group, which manages both DHC and Office Properties Income Trust, the real estate investment trusts that are seeking to merge but have faced significant opposition from shareholders.

Flat Footed had opposed the merger last month, saying the deal undervalues the REIT by 90% and there are better alternatives to an all-share deal.

Hedge fund D.E. Shaw has also said it would oppose the deal.

RMR Group did not immediately respond to a Reuters request for comment.

OPI and DHC announced the merger in April. (Reporting by Kannaki Deka in Bengaluru; Editing by Maju Samuel)