By Milana Vinn June 9 (Reuters) - TriNet Group TNET.N, an online payroll services provider with a market value of $5.8 billion, is exploring a potential sale of the company, according to people familiar with the matter. TriNet shares are up 44% so far this year, significantly outperforming an 11% return in the Russell 1000 index, as its business benefited from companies continuing to hire despite a spike in inflation. Concerns over a potential economic slowdown, however, fueled by the Federal Reserve raising interest rates, are clouding TriNet's financial outlook.