England's Kyle Walker in action with Wales' Neil Taylor
The 48-year-old told Alan Brazil's breakfast show that he would rest the 26-year-old against Slovakia to keep him in good condition for the knockout rounds.
"I think Walker should get a rest," Merson told Talksport. "I think he has been the best player in the tournament if I'm being honest.
"He has been absolutely outstanding. Bombing up and down the right, you need him fresh. He has definitely been our best player in the tournament."
Few would have expected a Gunners legend, and unsurprisingly then, a usual Spurs critic to be so effusive in his praise of a Tottenham man, but the former England midfielder has been thawing somewhat in that respect in recent months.
Merson was one of a number of pundits who appeared to be impressed with the style of football Mauricio Pochettino had Spurs playing last season, with the Lilywhites playing superb attacking football while also employing strong defensive resilience.
Southampton's Cuco Martina in action with Tottenham's Danny Rose
Hugely important in this system were fullbacks Danny Rose and Walker, and both have brought that form onto the international stage this summer, with Rose arguably joining Walker as one of England's top performers.
However, despite Walker impressing at right back, there will be plenty of other players who may feel they have a greater claim at player of the tournament so far, though things could of course change dramatically between this week and the final next month.
Not least Dimitri Payet, and West Ham supporters, with the France international sensational in his country's victories over Romania and Albania.
Though it is early stages, it will be interesting to see who Merson plumps for at the conclusion of the tournament.
France's Dimitri Payet celebrates after scoring their second goal