The 73-year-old shocked fans by leaving the Belgian out of the matchday squad for Sunday’s Scottish Premiership clash with Kilmarnock, but he confirmed in a pre-match interview that the midfielder is set for an extended period on the sidelines.

Engels has been a key player for Celtic so far this term, having already started 17 league games, but his team will now have to live without him for over a month.

The 22-year-old was withdrawn by O’Neill after just 32 minutes during the recent win over Livingston, and it has quickly become clear that the outcome of his issue is not favourable for the Bhoys.

Arne Engels could miss up to 10 games for Celtic

Engels has been crucial for Celtic in the middle of the park this season, as the club record buy has continued to stamp his mark on the team.

His importance was highlighted by the Bhoys’ desperation to keep hold of him in the final hours of the winter transfer window, despite Nottingham Forest tabling a lucrative offer of £25million on deadline day.

However, Engels’ injury really could not have come at a worse time for the Parkhead outfit, as they find themselves in the thick of the Scottish Premiership title race, while they are also still alive in the Europa League.

The 10 games that Engels could miss for Celtic.O’Neill’s end-of-March timeframe for Engels’ recovery is likely to see the youngster miss at least eight further games in all competitions (not including the trip to Kilmarnock), and that could even grow to 10 if his team find a way past Stuttgart in their Europa League play-off.

Concerningly for Celtic, that 10-game run contains two meetings with Rangers, one in the league and in the Scottish Cup, as well as difficult tests against both Hibernian and Motherwell.

Nottingham Forest to return for Engels this summer

Football Insider recently revealed that Nottingham Forest still have Engels on their shortlist of midfield targets, despite their failure to land him in the January window.

The Premier League side saw three separate bids knocked back by the Glasgow giants in the final stages of the window, but they still view him as a long-term target and are prepared to try again in the summer.

The Reds have already shown that they would be willing to splash the cash to add Engels to their squad, but they may see their pursuit fall short once again if they are relegated to the Championship at the end of the season.

Forest are strong admirers of the former Augsburg man, but both they and Celtic know that they are unlikely to be the only potential suitor for him.