Walker (shoulder) will make one more rehab start with Triple-A Lehigh Valley on Sunday before rejoining the Phillies' rotation, Todd Zolecki of MLB.com reports.
The Phillies had considered having Walker make his next appearance with the big club, but they opted to give him one more tune-up. That sets Walker up for his season debut next weekend in San Diego. Spencer Turnbull has pitched well in his place but could lose his rotation spot once Walker returns.