The Scotsman understands the German's displeasure in regards to training among the busy football schedule.
The Italian is currently on loan at Bologna.
Rajiv Van La Parra has recently returned to Wolverhampton Wanderers after completing a loan spell at Brighton & Hove Albion.
The 20-year-old is reportedly unhappy at Parc des Princes, and hopes to secure a move to the Premier League.
Andy Walker believes Celtic's recruitment has been poor in recent years.
Swansea City midfielder Jonjo Shelvey is said to be on the radars of Crystal Palace and Newcastle United.
Tottenham Hotspur are said to be impressed with the 23-year-old holding player.
Derby County had been linked with Aston Villa midfielder Jack Grealish.
Sunderland could be about to sign a new defender from the Bundesliga.
Ramiro Funes Mori moved to Everton from River Plate during the summer transfer window.