The Italian featured in Sunday night’s FA Cup fourth round defeat to Chelsea as a second half substitute after returning from a hamstring injury that has put him on the sidelines for two lengthy spells this campaign.
Forestieri, a £3 million recruit from Watford in 2015, has featured just 14 times this season in a stuttering campaign for the Owls winger.
And Agnew believes that patience will be key if Forestieri is to play a more prominent role in the conclusion of the 2018/19 season.
The interim Owls boss said: "He's a terrific player. He has been out for a while so we have to get him up to speed as quickly as possible.
"I'm sure Fernando will be ready for the Ipswich game after another week's training.
"Fernando had a hamstring injury and then a recurrence so we have to be mindful that there obviously has been a weakness in that area.”
Three-goal Forestieri suffered his first hamstring injury against Bristol City in October, which ruled him out of five matches, and then had a recurrence of the problem against Blackburn in December.
After missing the entirety of the congested period of Christmas fixtures, Forestieri returned in the closing stages against Chelsea and looked a lively addition to the Owls’ offensive unit.
And Agnew credited the hard work of the Wednesday medical team for the 29-year-old’s return.
He said: "The medical people have worked with him and they are more confident with where he is now with it.
"We just need to find a way of getting him back up to full speed as quickly as possible.”
Agnew will hand over the reigns as Owls boss this week as he moves into Steve Bruce’s coaching staff, joining Stephen Clemence and Lee Bullen who have also been involved in the former Aston Villa chief’s absence.
With the culmination of the season moving ever-closer, it is yet to be seen whether Wednesday will improve on last season’s 15th place finish in the Championship but Agnew insists the team will take the remainder of the season as it comes.
"We just have to look forward to Ipswich away and focus on one game at a time. We know the quality of players we have in the dressing room are more than capable of getting a result there.”