McDonald, who has played 26 times in all competitions for the League Two leaders this season, is out of contract in the summer.
Vale have inserted a recall clause in the deal enabling them to bring the 24-year-old back to Vale Park after the first 28 days of the loan.
McDonald began his career as a trainee at Manchester City and had a loan spell at Macclesfield before joining Walsall.
He left the Saddlers in June 2011 to join Vale on a free transfer, and has since made 59 appearances for the Burslem club.
