Paul Cook expects Doncaster to be crowned League Two champions.
But the Pompey boss insists his side will be ready to take advantage if Darren Ferguson’s men slip up.
The Blues, who secured promotion to League One with victory over Notts County on Easter Monday, travel to Mansfield on Saturday with an outside chance of finishing at the summit.
They trail leaders Donny by four points with two games remaining.
The Keepmoat Stadium outfit have lost their past two matches and third-placed Pompey have piled on the pressure.
Plymouth also have title credentials, sitting just two points behind Donny, in second.
Although Cook knows it’s a tough task, he has not yet given up on the silverware.
He said: ‘Of course we believe we can still win the title. Fergie’s having a right wobble, isn’t he!
‘He’s had a great season and I still think Doncaster will do it. We must keep winning and being honest.
‘Doncaster have had an unbelievable season.
‘They’ve been promoted for a long time and it’s hard to keep it going when the lads have had a sense of achievement.
‘If Doncaster were to win, that would kill us, but good luck to them.
‘We’ll keep going in the belief that we can.’