I would say if you can find someone else, then do so. If not just make sure you look it over before it goes? Maybe give him all your supporting info and let him know how you wnt it tailored? Is he fluent in his writing skills? LOR really need to focus on so many aspects of your abilities and since you cant submit a lot of them you gotta be pretty picky.
Who To Ask?
Most graduate programs require two or more letters of recommendation. Choosing your letter-writers often is difficult. Consider faculty members, administrators, internship/co-operative education supervisors, and employers. The persons you ask to write your letters should
know you well
know you long enough to write with authority
know your work
describe your work positively
have a high opinion of you
know where you are applying
know your educational and career goals
be able to favorably compare you with your peers
be well known
be able to write a good letter
Keep in mind that no one person will satisfy all of these criteria. Aim for a set of letters that cover the range of your skills. Ideally, letters should cover your academic and scholastic skills, research abilities and experiences, and applied experiences (e.g., co-operative education, internships, related work experience).