The Reds take on Barcelona at Wembley Stadium on Saturday evening, before travelling for a friendly clash with Mainz 05 at the Opel Arena on Sunday afternoon.
After a productive pre-season tour of the US, these outings will be the final test of Klopp’s side ahead of their 2016/17 campaign.
The German’s squad has been hampered with injuries this summer, however, with Matip and Grujic among a host of important players sidelined at points throughout pre-season.
Matip injured his ankle during Liverpool’s 2-0 win away to Wigan Athletic, while Grujic suffered concussion during the 1-0 defeat to Chelsea in Pasadena, California.
But speaking to reporters ahead of Saturday’s clash with Barcelona, Klopp confirmed they had both returned to training.
“Both are involved again,” he explained.
“Marko we had to wait for the green light. It wasn’t too serious, but we all use our brain, even for football!
“Joel has trained for three days now, so he will be involved too.”
However, Klopp continued to detail two prolonged absences, saying “Lucas [Leiva] isn’t available, and Joe Gomez of course too.”
Mamadou Sakho and Ovie Ejaria are also set to miss out against both Barcelona and Mainz, as they recover from Achilles and groin injuries respectively.
However, the return of Matip and Grujic will boost Klopp’s squad significantly, providing the 49-year-old with further options in both defence and midfield.
Neither are unlikely to start, though, with Dejan Lovren and Ragnar Klavan established at centre-back and the likes of Emre Can, Georginio Wijnaldum and Jordan Henderson available in the middle of the park.
Liverpool’s clash with Barcelona kicks off at 5.15pm (BST) on Saturday, with the Wembley clash set to be their biggest challenge of a busy pre-season schedule.