The Sunderland team captain has made an impressive start to his career on Wearside and was absent as the Black Cats fell to a 1-0 defeat to Burton Albion on Tuesday night.
Evans will almost certainly sit out the next two games, with Dan Neil and Luke O'Nien likely to continue their partnership in central midfield.
Johnson says the Northern Ireland midfielder has probably suffered from his late arrival this summer.
Most Popular
-
1
'Should have been sent off' - Sunderland fans fume at Ilias Chair as QPR goalkeeper Seny Deng scores
-
2
Sunderland 2 QPR 2: Highlights after Seny Dieng’s equaliser plus Ross Stewart and Ellis Simms goals
-
3
'Sublime': Phil Smith's Sunderland player ratings after Seny Dieng's late equaliser for QPR
-
4
Championship news: Sunderland’s rivals set to lose striker as Leicester City sign goalkeeper amid Daniel Iversen speculation
-
5
Sunderland's Championship rivals Wigan beat Rotherham to ex-SAFC striker signing
“I think the tough one with Corry is that because we recruited him late, I think we were chasing his minutes," Johnson said.
“He was getting fit through games at like 80% and it’s just tweaked.
“It’s a low grade hamstring, just on the side of the hamstring so we think it’s a quick healer but it’s probably going to be ten to 14 days."